Update hermetic build to use same proto files in BUILD.bazel in library generation

[alicejli]

googleapis/google-cloud-java#10802 is a new library generation request for visionai.v1.
However, it failed due to prediction.proto being an empty service (e.g. no RPCs). Related issue on fixing the generator to skip generation for empty services: #2750

It's excluded in the visionai.v1 BUILD file: https://github.com/googleapis/googleapis/blob/master/google/cloud/visionai/v1/BUILD.bazel#L23-L36

To fix this for the long-term, we should consider either parsing BUILD.bazel to get the list of protos or consider
integrating hermetic build scripts into Bazel so that the library generation will always use the same list of protos as the BUILD.bazel file.