use github.com/googleapis/googleapis directly

I am integrating this repository into my own Bazel project.

I am already using `github.com/googleapis/googleapis` as the `@googleapis` repository (the canonical one), which collides with the definition of the `@googleapis` repository for which a `BUILD.googleapis` file is vendored in `external` (the vendored).

I looked through the differences. I noticed that mainly the `@googleapis` vendored here ships with `cc_grpc_library` targets on top of a few things that the canonical repo already has.

It would probably be best to consolidate the two. Would like to open the discussion a bit.

Start by comparing the canonical github.com/googleapis/googleapis repository with the vendored external/BUILD.googleapis definition, focusing on the cc_grpc_library targets and other differences mentioned in the issue. Determine the maintainers' preferred consolidation approach; done would mean an agreed resolution for the @googleapis repository collision.

Written by the indexing model from the issue text.