Remove SSHUploadPack RPC
For #6410 (closed)
After we introduced the Sidechannel protocol, Gitaly's clients started to create Sidechannel variants for heavy RPCs such as PostUploadPack, PackObjectsHook, and SSHUploadPack. At the point of writing, nearly all clients migrated to the Sidechannel RPCs. There is no traffic to the original non-sidechannel variant of those RPCs.
We already removed PostUploadPack RPC, which is the counterpart of SSHUploadPack RPC for serving git via HTTP. This issue tracks the progress of deprecating and removing UploadPack RPC, in favor of the sidechannel version.
This MR removes SSHUploadPack RPC completely from the code base. It was marked as deprecated in !7324 (merged) (17.5). Now we target (17.8).