[vm, gc] Remove non-assert use of Contains during scavenging.

The scavenger should assume it visits pointers exactly once. This Contains was probably covering up a double visit that was probably fixed with the introduction of the compactor.

TEST=ci
Change-Id: I975cb27e1fedf9fbc0b0d46d33dd374204907037
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/261780
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>
diff --git a/runtime/vm/heap/scavenger.cc b/runtime/vm/heap/scavenger.cc
index 6ac1820..860825a 100644
--- a/runtime/vm/heap/scavenger.cc
+++ b/runtime/vm/heap/scavenger.cc
@@ -1228,9 +1228,6 @@
     return false;
   }
   uword raw_addr = UntaggedObject::ToAddr(raw_obj);
-  if (to_->Contains(raw_addr)) {
-    return false;
-  }
   uword header = *reinterpret_cast<uword*>(raw_addr);
   if (IsForwarding(header)) {
     *p = ForwardedObj(header);