stream: inline onwriteStateUpdate()

The function is very simple and is only called from `onwrite()`.

PR-URL: #27203
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Masashi Hirano <shisama07@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>

lib/_stream_writable.js

@@ -442,13 +442,6 @@ function onwriteError(stream, state, sync, er, cb) {
   }
 }
 
-function onwriteStateUpdate(state) {
-  state.writing = false;
-  state.writecb = null;
-  state.length -= state.writelen;
-  state.writelen = 0;
-}
-
 function onwrite(stream, er) {
   const state = stream._writableState;
   const sync = state.sync;
@@ -457,7 +450,10 @@ function onwrite(stream, er) {
   if (typeof cb !== 'function')
     throw new ERR_MULTIPLE_CALLBACK();
 
-  onwriteStateUpdate(state);
+  state.writing = false;
+  state.writecb = null;
+  state.length -= state.writelen;
+  state.writelen = 0;
 
   if (er)
     onwriteError(stream, state, sync, er, cb);