Replace wiki_delete_page RPC [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

In this MR we replace the existing RPC wiki_delete_page with the existing RPC used in Repository#delete_file (behind a feature flag). If we can do that, we will be able to remove the former RPC.

Ref #324385 (closed)

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have not included a changelog entry because it's behind a feature flag.
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