Remove ProtobufImport
Remove ProtobufImport

We don't support ReviewDb anymore and hence we also don't support
importing data into ReviewDb anymore.

With this removal, we don't mention/use ProtobufCodec anywhere in
our code base anymore.

Change-Id: If3dc580d0c679fe48c6c3337dcc835b3657a88ee

qtproject/qtqa-gerrit,GerritCodeReview/gerrit,qtproject/qtqa-gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,qtproject/qtqa-gerrit,qtproject/qtqa-gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,qtproject/qtqa-gerrit,qtproject/qtqa-gerrit,qtproject/qtqa-gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit