It is a little shorter and cheaper[1] than the equivalent
"mov sp,bp; pop bp".

Also remove support for the 'enter' instruction, since
- it is unused,
- it is neither shorter nor cheaper than the corresponding
  push and mov (in fact more expensive[1]), and
- our disassembler doesn't support it.

[1] See https://www.agner.org/optimize/instruction_tables.pdf

Change-Id: I6c99c2f3e53081aea55445a54e18eaf45baa79c2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2482822
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70660}