Revert "[LV] Unconditionally branch from middle to scalar preheader if the...

Revert "[LV] Unconditionally branch from middle to scalar preheader if the scalar loop must execute (try 3)"

This reverts commit 6d3e3ae8.

Still seeing PPC build bot failures, and one arm self host bot failing.  I'm officially stumped, and need help from a bot owner to reduce.