This is a follow on ticket from WT-14040.

We trigger live restore clean up when the final background migration thread terminates after copying all files. If we restart WiredTiger in the CLEAN_UP or COMPLETE states this is wasteful, as we spin up the background threads just to immediately kill them.

This ticket is to add a code path where we directly call clean up instead of spinning up migration threads when WiredTiger is in the CLEAN_UP or COMPLETE states on startup