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>

Author: ChALkeR

lib/internal/fs/promises.js

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