git-remote-entire: unify git protocol agent and HTTP User-Agent

The previous commit stamped the HTTP User-Agent with versioninfo.Version while the git protocol agent kept its prior versioninfo.Commit format, leaving two different identifiers for the same binary. Use the version-stamped form for both — server-side log analysis can correlate git protocol agent and HTTP access-log entries without translation, and the conventional binary/version shape matches what the rest of the entire HTTP clients advertise.