Rather than doing nop elision in the peephole optimizer, be smarter about
emitting nops for elided register transfers in the bytecode optimizer.

BUG=v8:6194

Change-Id: Ib1a7168a0d143e4f2da7c6d43080998793c30822
Reviewed-on: https://chromium-review.googlesource.com/468929
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44479}