Remove old 15_11 fix
What does this MR do and why?
In !121188 (merged) we added a special rake task to fix the schema_migrations
table for folks upgrading 15.11 minor versions. This task is no longer needed.
In !121188 (merged) we added a special rake task to fix the schema_migrations
table for folks upgrading 15.11 minor versions. This task is no longer needed.