Remove unused Pages admin API settings
In !3444 (comment 194217889) it was suggested that we remove the code related to unfinished and never used Pages - GitLab gRPC API.
This MR removes the related code from Omnibus (basically an undo of !2466 (merged)), Pages was done in gitlab!18172 (merged) and GitLab in gitlab!18172 (merged)
Once this is merged I'll update !3444 (closed).
Edited by GitLab Release Tools Bot