Remove use of current_cc_toolchain

Based on https://github.com/bazelbuild/bazel/issues/26282, this is a request to remove the use of `@bazel_tools//tools/cpp:current_cc_toolchain` in rules_python (specifically, [here](https://github.com/bazel-contrib/rules_python/blob/e225a1eddd6055b08cb832f7d4e73922d5f7d956/python/private/attributes.bzl#L162)).