[compiler, ia32] Don't check if to-be-moved heap object is in new space.

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}

src/compiler/ia32/code-generator-ia32.cc

@@ -2559,13 +2559,7 @@ void CodeGenerator::AssembleMove(InstructionOperand* source,
       } else {
         DCHECK(destination->IsStackSlot());
         Operand dst = g.ToOperand(destination);
-        AllowDeferredHandleDereference embedding_raw_address;
-        if (isolate()->heap()->InNewSpace(*src)) {
-          __ PushHeapObject(src);
-          __ pop(dst);
-        } else {
-          __ mov(dst, src);
-        }
+        __ mov(dst, src);
       }
     } else if (destination->IsRegister()) {
       Register dst = g.ToRegister(destination);