Revert to non-forked grpcio-compiler (#5842)
Revert to non-forked grpcio-compiler (#5842)

protobuf re-released 1.5 as 1.7 undoing the breaking changes.
baroquebobcat/pants,pantsbuild/pants,tdyas/pants,wisechengyi/pants,tdyas/pants,pantsbuild/pants,wisechengyi/pants,twitter/pants,twitter/pants,baroquebobcat/pants,pantsbuild/pants,baroquebobcat/pants,twitter/pants,benjyw/pants,pantsbuild/pants,tdyas/pants,twitter/pants,wisechengyi/pants,twitter/pants,jsirois/pants,benjyw/pants,tdyas/pants,baroquebobcat/pants,pantsbuild/pants,baroquebobcat/pants,tdyas/pants,benjyw/pants,twitter/pants,tdyas/pants,benjyw/pants,baroquebobcat/pants,twitter/pants,wisechengyi/pants,pantsbuild/pants,benjyw/pants,wisechengyi/pants,jsirois/pants,wisechengyi/pants,tdyas/pants,baroquebobcat/pants,tdyas/pants,pantsbuild/pants,wisechengyi/pants,baroquebobcat/pants,baroquebobcat/pants,twitter/pants,benjyw/pants,jsirois/pants,benjyw/pants,wisechengyi/pants,tdyas/pants,twitter/pants,wisechengyi/pants