go_default_library should not be a go_proto_library

[tyler-french]

naming this: https://github.com/bazelbuild/buildtools/blob/master/build_proto/BUILD.bazel#L22 go_default_library is causing issues:

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
link: package conflict error: github.com/bazelbuild/buildtools/lang: package imports github.com/bazelbuild/buildtools/build_proto
          was compiled with: @@gazelle~override~go_deps~com_github_bazelbuild_buildtools//build_proto:build_proto
        but was linked with: @@gazelle~override~go_deps~com_github_bazelbuild_buildtools//build_proto:go_default_library
See https://github.com/bazelbuild/rules_go/issues/1877.

We should not be calling a go_proto_library( go_default_library because it prevents adding the alias. See the api_proto file as an example: https://github.com/bazelbuild/buildtools/blob/master/api_proto/BUILD.bazel

[vladmos]

cc @fmeum