With FCG no longer able to deoptimize, we can remove the "push" version
of output frame state combine, as deoptimisation to bytecode is always
the PokeAt variant.

Bug: v8:6409
Change-Id: I9b6d38a7441ca834835615c238228fa8a75a027b
Reviewed-on: https://chromium-review.googlesource.com/557866
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46355}