SDK Ghost page clean up

In the original rush to write the SDK 3 docs from scratch, many templates were either populated or sketched out, but some remained unfilled as plans were changed...

Page stubs that were left as foo.adoc get built as foo.html - and although not shown in the nav, will get indexed by Google.

This task is to go through each SDK's repo, find pages that aren't used, and check if they are still needed - in which case add a comment note linking to the DOC JIRA.

For example of redundant page stub, see  DOC-8525 - it looks like the planned example code will not appear - in this case, it would be useful to add a page alias to https://docs.couchbase.com/dotnet-sdk/current/concept-docs/durability-replication-failure-considerations.html#durable-writes for now, to pick up any indexed searches that are landing there.