BytecodeRegisterOptimizer had special handling for the case when parameters
is 0. This is not possible from valid javascript. It exists because some
tests do not take this into account. Fixed tests and removed the special
handling.

Also removed a TODO, which is already done here:
https://codereview.chromium.org/2227203002/

Bug: v8:4280,v8:6325
Change-Id: Idc17af12ad9292c13a6677aa4c8b88d21f4adf81
Reviewed-on: https://chromium-review.googlesource.com/490308
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45036}