stream: replace object sentinel with symbol

Signed-off-by: James M Snell <jasnell@gmail.com>

Author: jasnell

lib/internal/streams/iter/consumers.js

@@ -18,6 +18,7 @@ const {
   Promise,
   PromisePrototypeThen,
   SafePromiseAllReturnVoid,
+  Symbol,
   SymbolAsyncIterator,
   TypedArrayPrototypeGetBuffer,
   TypedArrayPrototypeGetByteLength,
@@ -401,7 +402,7 @@ function ondrain(drainable) {
 // Merge Utility
 // =============================================================================
 
-const kNoMergeError = { __proto__: null };
+const kNoMergeError = Symbol('kNoMergeError');
 
 /**
  * Merge multiple async iterables by yielding values in temporal order.