This removes special casing in the handling of {RelocInfo::CODE_TARGET}
for cases where such references appeared in {WasmCode}. Such references
can only appear in real {Code} objects and also only target real {Code}
objects by now.

R=clemensh@chromium.org

Change-Id: I87c55c60cd6344bb67fa8c8d04b66fb523d07ba7
Reviewed-on: https://chromium-review.googlesource.com/1104680
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53848}