Delete tests of dead pre-GA code

src/python/grpcio/tests/tests.json

...thon/grpcio/tests/unit/_adapter/_intermediary_low_test.py

src/python/grpcio/tests/unit/_adapter/_low_test.py

...grpcio/tests/unit/_core_over_links_base_interface_test.py

...s/unit/_crust_over_core_over_links_face_interface_test.py

.../grpcio/tests/unit/_links/_lonely_invocation_link_test.py

src/python/grpcio/tests/unit/_links/_transmission_test.py

...ts/unit/framework/_crust_over_core_face_interface_test.py

.../grpcio/tests/unit/framework/core/_base_interface_test.py

...hon/grpcio/tests/unit/framework/foundation/_later_test.py