Removed support for 3m, 4m induced methods.

Details:
- Removed support for all induced methods except for 1m. This included
  removing code related to 3mh, 3m1, 4mh, 4m1a, and 4m1b as well as any
  code that existed only to support those implementations. These
  implementations were rarely used and posed code maintenance challenges
  for BLIS's maintainers going forward.
- Removed reference kernels for packm that pack 3m and 4m micropanels,
  and removed 3m/4m-related code from bli_cntx_ref.c.
- Removed support for 3m/4m from the code in frame/ind, then reorganized
  and streamlined the remaining code in that directory. The *ind(),
  *nat(), and *1m() APIs were all removed. (These additional API layers
  no longer made as much sense with only one induced method (1m) being
  supported.) The bli_ind.c file (and header) were moved to frame/base
  and bli_l3_ind.c (and header) and bli_l3_ind_tapi.h were moved to
  frame/3.
- Removed 3m/4m support from the code in frame/1m/packm.
- Removed 3m/4m support from trmm/trsm macrokernels and simplified some
  pointer arithmetic that was previously expressed in terms of the
  bli_ptr_inc_by_frac() static inline function (whose definition was
  also removed).
- Removed the following subdirectories of level-0 macro headers from
  frame/include/level0: ri3, rih, ri, ro, rpi. The level-0 scalar macros
  defined in these directories were used exclusively for 3m and 4m
  method codes.
- Simplified bli_cntx_set_blkszs() and bli_cntx_set_ind_blkszs() in
  light of 1m being the only induced method left within BLIS.
- Removed dt_on_output field within auxinfo_t and its associated
  accessor functions.
- Re-indexed the 1e/1r pack schemas after removing those associated with
  variants of the 3m and 4m methods. This leaves two bits unused within
  the pack format portion of the schema bitfield. (See bli_type_defs.h
  for more info.)
- Spun off the basic and expert interfaces to the object and typed APIs
  into separate files: bli_l3_oapi.c and bli_l3_oapi_ex.c; bli_l3_tapi.c
  and bli_l3_tapi_ex.c.
- Moved the level-3 operation-specific _check function calls from the
  operations' _front() functions to the corresponding _ex() function of
  the object API. (This change roughly maintains where the _check()
  functions are called in the call stack but lays the groundwork for
  future changes that may come to the level-3 object APIs.) Minor
  modifications to bli_l3_check.c to allow the check() functions to be
  called from the expert interface APIs.
- Removed support within the testsuite for testing the aforementioned
  induced methods, and updated the standalone test drivers in the 'test'
  directory so reflect the retirement of those induced methods.
- Modified the sandbox contract so that the user is obliged to define
  bli_gemm_ex() instead of bli_gemmnat(). (This change was made in light
  of the *nat() functions no longer existing.) Also updated the existing
  'power10' and 'gemmlike' sandboxes to come into compliance with the
  new sandbox rules.
- Updated BLISObjectAPI.md, BLISTypedAPI.md, Testsuite.md documentation
  to reflect the retirement of 3m/4m, and also modified Sandboxes.md to
  bring the document into alignment with new conventions.
- Updated various comments; removed segments of commented-out code.

docs/BLISObjectAPI.md

@@ -2336,16 +2336,9 @@ char* bli_info_get_trsm_u_ukr_impl_string( ind_t method, num_t dt )
 ```
 
 Possible implementation (ie: the `ind_t method` argument) types are:
- * `BLIS_3MH`: Implementation based on the 3m method applied at the highest level, outside the 5th loop around the microkernel.
- * `BLIS_3M1`: Implementation based on the 3m method applied within the 1st loop around the microkernel.
- * `BLIS_4MH`: Implementation based on the 4m method applied at the highest level, outside the 5th loop around the microkernel.
- * `BLIS_4M1B`: Implementation based on the 4m method applied within the 1st loop around the microkernel. Computation is ordered such that the 1st loop is fissured into two loops, the first of which multiplies the real part of the current micropanel of packed matrix B (against all real and imaginary parts of packed matrix A), and the second of which multiplies the imaginary part of the current micropanel of packed matrix B.
- * `BLIS_4M1A`: Implementation based on the 4m method applied within the 1st loop around the microkernel. Computation is ordered such that real and imaginary components of the current micropanels are completely used before proceeding to the next virtual microkernel invocation.
  * `BLIS_1M`: Implementation based on the 1m method. (This is the default induced method when real domain kernels are present but complex kernels are missing.)
  * `BLIS_NAT`: Implementation based on "native" execution (ie: NOT an induced method).
 
-**NOTE**: `BLIS_3M3` and `BLIS_3M2` have been deprecated from the `typedef enum` of `ind_t`, and `BLIS_4M1B` is also effectively no longer available, though the `typedef enum` value still exists.
-
 Possible microkernel types (ie: the return values for `bli_info_get_*_ukr_impl_string()`) are:
  * `BLIS_REFERENCE_UKERNEL` (`"refrnce"`): This value is returned when the queried microkernel is provided by the reference implementation.
  * `BLIS_VIRTUAL_UKERNEL` (`"virtual"`): This value is returned when the queried microkernel is driven by a the "virtual" microkernel provided by an induced method. This happens for any `method` value that is not `BLIS_NAT` (ie: native), but only applies to the complex domain.