Fix build time note: [RhinoNodeDetachFirstChild] Simplification

Changes:
fullChainStart.getFirstChild().detach();
to:
fullChainStart.removeFirstChild();
PiperOrigin-RevId: 325807540

Author: rishipal

src/com/google/javascript/jscomp/OptionalChainRewriter.java

@@ -204,7 +204,7 @@ private Node rewriteInitialSegment(final Node fullChainStart, final Node fullCha
       final Node thisValue = receiverNode.getFirstChild();
       final Node tmpThisNode = getSubExprNameNode(thisValue);
       final Node tmpReceiverNode = getSubExprNameNode(receiverNode);
-      receiverNode = fullChainStart.getFirstChild().detach();
+      receiverNode = fullChainStart.removeFirstChild();
       fullChainStart.addChildToFront(tmpThisNode);
       fullChainStart.addChildToFront(
           astFactory