fs: remove broken code in promises/write

That code expects the last argument to be a callback.
When it's not a callback, it shifts arguments, defaulting
encoding to 'utf-8', which is clearly broken.

Old signature: (fd, string[, position[, encoding]], callback)
New signature: (fd, string[, position[, encoding]])

PR-URL: #20407
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Jamie Davis <davisjam@vt.edu>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

lib/internal/fs/promises.js

@@ -242,15 +242,6 @@ async function write(handle, buffer, offset, length, position) {
 
   if (typeof buffer !== 'string')
     buffer += '';
-  if (typeof position !== 'function') {
-    if (typeof offset === 'function') {
-      position = offset;
-      offset = null;
-    } else {
-      position = length;
-    }
-    length = 'utf8';
-  }
   const bytesWritten = (await binding.writeString(handle.fd, buffer, offset,
                                                   length, kUsePromises)) || 0;
   return { bytesWritten, buffer };