In his book The Art of War for Writers, James Scott Bell says,
[E]very character in every scene must have an objective, otherwise he shouldn’t be there. Replace him with a chair.
Review your WIP. If you find a character(s) who is superfluous? Do as Bell suggests, rewrite the scene and cut the character.
Now reread the scene. Is it stronger, weaker, mediocre? Revise until you are satisfied. It may mean putting the character back in, but do that only after you’ve determined his/her objective.