Revert "Adding documentation with associated test: Using py::classh but with fallback to classic pybind11"

This reverts commit 49f8f60.

The direct commit was accidental. I meant to create a PR.

Author: rwgk

README_smart_holder.rst

@@ -164,17 +164,6 @@ of interest have made the switch, because then the code will continue to
 work in either mode.
 
 
-Using py::classh but with fallback to classic pybind11
-------------------------------------------------------
-
-This could be viewed as super-conservative mode, for situations in which
-compatibility with classic pybind11 (without smart_holder) is needed for
-some period of time. The main idea is to enable use of ``py::classh``
-and the associated ``PYBIND11_SMART_HOLDER_TYPE_CASTERS`` macro while
-still being able to build the same code with classic pybind11. Please see
-tests/test_classh_mock.cpp for an example.
-
-
 Trampolines and std::unique_ptr
 -------------------------------
 

tests/CMakeLists.txt

@@ -112,7 +112,6 @@ set(PYBIND11_TEST_FILES
     test_class_sh_trampoline_unique_ptr.cpp
     test_class_sh_unique_ptr_member.cpp
     test_class_sh_virtual_py_cpp_mix.cpp
-    test_classh_mock.cpp
     test_constants_and_functions.cpp
     test_copy_move.cpp
     test_custom_type_casters.cpp