Drop reinstall of google-protobuf and use precompiled gems

What does this MR do?

!1372 (merged) reinstalled the google-protobuf gem because as shown in #2042 (closed), the precompiled gem of google-protobuf didn't work on CentOS 6 due to glibc compatibility issues.

However, since then we've dropped support for CentOS 6. The precompiled gem is built with manylinux2014_x86_64, which is CentOS 7. We already use precompiled gems for grpc (which also compiles google-protobuf), prometheus-client-mmap, and nokogiri, so there's no reason google-protobuf should be an exception.

Using the precompiled gem speeds build times and avoids build issues with CentOS 7 and SLES 12.5.

Related issues

Relates to #7818 (closed)

Checklist

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