This commit removes a document originally created to troubleshoot
upgrades from Open Source to Enterprise.
Since we no longer support Open Source, this document is now redundant.
Fixes https://github.com/scylladb/scylladb/issues/28246
Closes scylladb/scylladb#28248
(cherry picked from commit 84281f900f)
Closes scylladb/scylladb#28360