wiki: Remove GetPageVersions RPC
There's one client that uses PageVersions, Rails. This RPC ultimately meant; what versions of a certain path exists for a repository. There already was an RPC for that, and now Rails uses that one. This means we can remove this RPC a release after the Rails code has been release.
This change removes most of the dead code, probably not all but the risk/reward ratio of removing code in the sidecar is high until we remove the sidecar alltogether.
Upstream changes: gitlab!61459 (merged)
Edited by Zeger-Jan van de Weg