[turbofan] new escape analysis reducer: remove duplicate line and add a DCHECK

Bug: 
Change-Id: Ifd233c9b592c784d6326d3663c491e5e32e9ddeb
Reviewed-on: https://chromium-review.googlesource.com/600047Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47118}

src/compiler/new-escape-analysis-reducer.cc

@@ -62,7 +62,7 @@ Reduction NewEscapeAnalysisReducer::Reduce(Node* node) {
   if (Node* replacement = analysis_result().GetReplacementOf(node)) {
     DCHECK(node->opcode() != IrOpcode::kAllocate &&
            node->opcode() != IrOpcode::kFinishRegion);
-    RelaxEffectsAndControls(node);
+    DCHECK_NE(replacement, node);
     if (replacement != jsgraph()->Dead()) {
       replacement = MaybeGuard(node, replacement);
     }