On ia32, AssembleMove used to emit different code depending on whether
the to-be-moved heap object is in new space or not. This may have been
necessary in the past but is no longer. Moreoever, it's incompatible
with running off-thread. With this CL, we don't do the new-space check
and just emit a mov.

R=mstarzinger@chromium.org

Bug: v8:6048
Change-Id: I93abd61a5f290311a431edee3d4fa0a240d52085
Reviewed-on: https://chromium-review.googlesource.com/519248Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45653}