Revert "Redesigned virtual call mechanism and user-facing syntax (breaking change!)"

This reverts commit 86d825f330.

example/issues.cpp

@@ -42,7 +42,8 @@ void init_issues(py::module &m) {
         }
     };
 
-    py::class_<Base, std::unique_ptr<Base>, DispatchIssue>(m2, "DispatchIssue")
+    py::class_<DispatchIssue> base(m2, "DispatchIssue");
+    base.alias<Base>()
         .def(py::init<>())
         .def("dispatch", &Base::dispatch);
 
@@ -107,35 +108,4 @@ void init_issues(py::module &m) {
     // (no id): don't cast doubles to ints
     m2.def("expect_float", [](float f) { return f; });
     m2.def("expect_int", [](int i) { return i; });
-
-    // (no id): don't invoke Python dispatch code when instantiating C++
-    // classes that were not extended on the Python side
-    struct A {
-        virtual ~A() {}
-        virtual void f() { std::cout << "A.f()" << std::endl; }
-    };
-
-    struct PyA : A {
-        PyA() { std::cout << "PyA.PyA()" << std::endl; }
-
-        void f() override {
-            std::cout << "PyA.f()" << std::endl;
-            PYBIND11_OVERLOAD(void, A, f);
-        }
-    };
-
-    auto call_f = [](A *a) { a->f(); };
-
-	pybind11::class_<A, std::unique_ptr<A>, PyA>(m2, "A")
-	    .def(py::init<>())
-	    .def("f", &A::f);
-
-	 m2.def("call_f", call_f);
-
-    try {
-        py::class_<Placeholder>(m2, "Placeholder");
-        throw std::logic_error("Expected an exception!");
-    } catch (std::runtime_error &) {
-        /* All good */
-    }
 }