Now that OSR is done during graph building, we no longer have to
special-case OSR loops in the loop assignment analysis, as we no longer
have the restriction that registers are 'assigned' an OSRValue inside
the loop.

Bug: v8:6518
Change-Id: Ib4fa139091d77efa16246ddc6e63a10cbb877ee4
Reviewed-on: https://chromium-review.googlesource.com/615167Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47367}