Revert "Fully support pairs in the register allocator."

Libcore tests fail.

This reverts commit 41aedbb684ccef76ff8373f39aba606ce4cb3194.

Change-Id: I2572f120d4bbaeb7a4d4cbfd47ab00c9ea39ac6c
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index dc8a7ee..fa51f27 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -2802,25 +2802,18 @@
       AddMove(source.ToLow(), destination.ToLow(), instruction);
       AddMove(source.ToHigh(), destination.ToHigh(), nullptr);
     } else if (source.IsPair()) {
-      DCHECK(destination.IsDoubleStackSlot()) << destination;
+      DCHECK(destination.IsDoubleStackSlot());
       AddMove(source.ToLow(), Location::StackSlot(destination.GetStackIndex()), instruction);
       AddMove(source.ToHigh(), Location::StackSlot(destination.GetHighStackIndex(4)), nullptr);
     } else if (destination.IsPair()) {
-      if (source.IsConstant()) {
-        // We put the same constant in the move. The code generator will handle which
-        // low or high part to use.
-        AddMove(source, destination.ToLow(), instruction);
-        AddMove(source, destination.ToHigh(), nullptr);
-      } else {
-        DCHECK(source.IsDoubleStackSlot());
-        AddMove(Location::StackSlot(source.GetStackIndex()), destination.ToLow(), instruction);
-        // TODO: rewrite GetHighStackIndex to not require a word size. It's supposed to
-        // always be 4.
-        static constexpr int kHighOffset = 4;
-        AddMove(Location::StackSlot(source.GetHighStackIndex(kHighOffset)),
-                destination.ToHigh(),
-                nullptr);
-      }
+      DCHECK(source.IsDoubleStackSlot());
+      AddMove(Location::StackSlot(source.GetStackIndex()), destination.ToLow(), instruction);
+      // TODO: rewrite GetHighStackIndex to not require a word size. It's supposed to
+      // always be 4.
+      static constexpr int kHighOffset = 4;
+      AddMove(Location::StackSlot(source.GetHighStackIndex(kHighOffset)),
+              destination.ToHigh(),
+              nullptr);
     } else {
       if (kIsDebugBuild) {
         if (instruction != nullptr) {