fs: refactor to remove redundant validation

The function makeCallback already calls validateCallback, so the call
inside copyFile can be removed.

PR-URL: #36984
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/fs.js

@@ -2036,8 +2036,6 @@ function copyFile(src, dest, mode, callback) {
   if (typeof mode === 'function') {
     callback = mode;
     mode = 0;
-  } else {
-    validateCallback(callback);
   }
 
   src = getValidatedPath(src, 'src');