Moves the logic for eliding non-effectful accumulator load elision from the
peephole optimizer to the BytecodeArrayWriter.

BUG=v8:6194

Change-Id: I05fbe4ee8ac340e5c355285d0b47e4a9d52fd0a8
Reviewed-on: https://chromium-review.googlesource.com/469828
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44560}