Remove deprecated second argument to SendPort.send().

runtime/lib/isolate_patch.dart

Index: runtime/lib/isolate_patch.dart
diff --git a/runtime/lib/isolate_patch.dart b/runtime/lib/isolate_patch.dart
index 6022b076481064e7a995dfd70bb7c6807ca69a99..0a1a9ab28286cbb5aeda30032f35d67f9d04cc7d 100644
--- a/runtime/lib/isolate_patch.dart
+++ b/runtime/lib/isolate_patch.dart
@@ -110,13 +110,8 @@ class _RawReceivePortImpl implements RawReceivePort {
 
 class _SendPortImpl implements SendPort {
   /*--- public interface ---*/
-  void send(var message, [SendPort replyTo = null]) {
-    this._sendNow(message, replyTo);
-  }
-
-  void _sendNow(var message, SendPort replyTo) {
-    int replyId = (replyTo == null) ? 0 : replyTo._id;
-    _sendInternal(_id, replyId, message);
+  void send(var message) {
+    _sendInternal(_id, 0, message);
   }
 
   bool operator==(var other) {
@@ -145,6 +140,7 @@ class _SendPortImpl implements SendPort {
 
   // Forward the implementation of sending messages to the VM. Only port ids
   // are being handed to the VM.
+  // TODO(14731): Remove replyId argument.
   static _sendInternal(int sendId, int replyId, var message)
       native "SendPortImpl_sendInternal_";