This commit removes the information about the recommended way of upgrading
ScyllaDB images - by updating ScyllaDB and OS packages in one step. This upgrade
procedure is not supported (it was implemented, but then reverted).
Refs https://github.com/scylladb/scylladb/issues/15733
Closes scylladb/scylladb#21876
Fixes https://github.com/scylladb/scylla-enterprise/issues/5041
Fixes https://github.com/scylladb/scylladb/issues/21898
(cherry picked from commit 98860905d8)