Revert "Merge pull request #20097 from gnossen/dual_version_python_tests"

BUILD

bazel/grpc_build_system.bzl

bazel/grpc_deps.bzl

bazel/grpc_python_deps.bzl

bazel/python_rules.bzl

examples/python/auth/BUILD.bazel

examples/python/cancellation/BUILD.bazel

examples/python/compression/BUILD.bazel

examples/python/debug/BUILD.bazel

examples/python/errors/BUILD.bazel

examples/python/multiprocessing/BUILD

examples/python/wait_for_ready/BUILD.bazel

src/python/grpcio_tests/tests/channelz/BUILD.bazel

src/python/grpcio_tests/tests/health_check/BUILD.bazel

src/python/grpcio_tests/tests/interop/BUILD.bazel

src/python/grpcio_tests/tests/reflection/BUILD.bazel

src/python/grpcio_tests/tests/status/BUILD.bazel

src/python/grpcio_tests/tests/unit/BUILD.bazel

src/python/grpcio_tests/tests/unit/_cython/BUILD.bazel

.../grpcio_tests/tests/unit/framework/foundation/BUILD.bazel