Now that all builtins are embedded, it is no longer needed to have a
fallback variant where WebAssembly runtime stubs tail-call existing
(non-embedded) builtins, just call the (embedded) builtin directly.

R=clemensb@chromium.org
BUG=v8:6666,v8:9810

Change-Id: Id8a2b2089cabc77f841f484986d8212ca2918ef4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1883550
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64581}