chore: clean up consumed .server-changes/ files from v4.4.5

Cleanup workflow stranded these files when v4.4.5 (#3406) was merged:
the changesets-pr workflow's cancel-in-progress concurrency policy
killed the update-lockfile job (which holds the .server-changes/
cleanup step) on the post-merge run. PR #3505 fixes the underlying
race by collapsing the cleanup into changeset:version itself; this
PR clears the leftover files so the v4.4.6 release PR (#3501) only
lists genuinely new server changes.

Keeps fix-rollback-schedule-sync.md (#3468) — that is the only
server change new in 4.4.6.

Author: ericallam