Make cseKill tolerate temps from non-cseable instructions

If you have a killsSources instruction where one of the
sources comes from a non-CSEable instruction that has extra data, this
currently aborts because it tries to call hash() for the extra data
but can't.

hphp/runtime/vm/translator/hopt/tracebuilder.cpp

@@ -1497,7 +1497,9 @@ void TraceBuilder::cseInsert(IRInstruction* inst) {
 }
 
 void TraceBuilder::cseKill(SSATmp* src) {
-  getCSEHashTable(src->getInstruction())->erase(src);
+  if (src->getInstruction()->canCSE()) {
+    getCSEHashTable(src->getInstruction())->erase(src);
+  }
 }
 
 SSATmp* TraceBuilder::cseLookup(IRInstruction* inst) {