[turbofan] Remove hack for dead nodes from JSGenericLowering.

Now that the graph is being trimmed after generic lowering, we can drop
this workaround. The diamond will no longer confuse the scheduler.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/1191913002

Cr-Commit-Position: refs/heads/master@{#29081}

src/compiler/js-generic-lowering.cc

@@ -196,9 +196,6 @@ void JSGenericLowering::ReplaceWithCompareIC(Node* node, Token::Value token) {
 
   // Finally patch the original node to select a boolean.
   NodeProperties::ReplaceUses(node, node, compare, compare, compare);
-  // TODO(mstarzinger): Just a work-around because SelectLowering might
-  // otherwise introduce a Phi without any uses, making Scheduler unhappy.
-  if (node->UseCount() == 0) return;
   node->TrimInputCount(3);
   node->ReplaceInput(0, booleanize);
   node->ReplaceInput(1, true_value);