Cleanups to testsuite, input.operations format.

Details:
- Removed the line in each operation entry in input.operations titled
  "test sequential front-end" and the corresponding support for the lines
  in the testsuite input parsing code. This line was included in the some
  of the earliest versions of the testsuite, back when I intended to
  eventually have separate multithreaded APIs. Specifically, I envisioned
  that multithreaded and sequential testing could be enabled or disabled
  on an operation level. However, BLIS evolved in a different direction
  and still does not have multithreaded-specific APIs (even if it will
  eventually someday). But even if it did have such APIs, I doubt I would
  allow the user to enable/disable them on an operation level. Thus, this
  was a zombie future parameter that was never used and never made sense
  to begin with. The one instance of the front_seq variable, used in the
  various libblis_test_<operation>() functions to guard the call to the
  operation test driver, that remains was commented out instead of
  deleted so that someday it could be easily changed via sed, if desired.
- Various minor cleanups to the testsuite code, including consolidating
  use of DISABLE and DISABLE_ALL and reexpressing certain conditional
  expressions in the libblis_test_<operation>() functions in terms of
  boolean functions.

testsuite/src/test_axpy2v.c

@@ -114,17 +114,17 @@ void libblis_test_axpy2v
 {
 
 	// Return early if this test has already been done.
-	if ( op->test_done == TRUE ) return;
+	if ( libblis_test_op_is_done( op ) ) return;
 
 	// Return early if operation is disabled.
 	if ( libblis_test_op_is_disabled( op ) ||
-	     op->ops->l1f_over == DISABLE_ALL ) return;
+	     libblis_test_l1f_is_disabled( op ) ) return;
 
 	// Call dependencies first.
 	if ( TRUE ) libblis_test_axpy2v_deps( params, op );
 
 	// Execute the test driver for each implementation requested.
-	if ( op->front_seq == ENABLE )
+	//if ( op->front_seq == ENABLE )
 	{
 		libblis_test_op_driver( params,
 		                        op,