stream: delete unused code

In implementation of `stream.Writable`, `writable._write()` is always called with a callback that is `_writableState.onwrite()`. And In `afterTransform()`, `ts.writechunk` and `ts.writecb` are assigned to null. So, `ts.writecb` is a true value if `ts.writechunk` isn't null. PR-URL: #18278 Reviewed-By: Matteo Collina <[email protected]> Reviewed-By: Ruben Bridgewater <[email protected]> Reviewed-By: James M Snell <[email protected]>

Author: 陈刚

lib/_stream_transform.js

@@ -180,7 +180,7 @@ Transform.prototype._write = function(chunk, encoding, cb){
 Transform.prototype._read=function(n){
 varts=this._transformState;
 
-if(ts.writechunk!==null&&ts.writecb&&!ts.transforming){
+if(ts.writechunk!==null&&!ts.transforming){
 ts.transforming=true;
 this._transform(ts.writechunk,ts.writeencoding,ts.afterTransform);
 }else{