This prologue is not needed any more now that we have the jump table.
If optimized code exists, we will not even enter the Liftoff code any
more, but instead jump to the optimized code right away.
This also allows to remove the {WASM_CODE_TABLE_ENTRY} relocation info
kind.

R=mstarzinger@chromium.org

Bug: v8:7758
Change-Id: I0449693d7434088fb264104fe59365d7ca2b74c6
Reviewed-on: https://chromium-review.googlesource.com/1110222Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53954}