Power cell overlay now updates when exiting an object's contents (#85079)

## About The Pull Request
The charge indicator overlay on power cells is now properly updated when
the cell is charged/discharged. Before, you could use a power cell until
it's empty and the overlay wouldn't change at all.
## Why It's Good For The Game
The overlay is there to indicate the charge of the cell. It should work.
## Changelog
🆑
fix: The charge indicators on power cells now work properly.
code: Removed some now redundant power cell appearance updates
/🆑

---------

Co-authored-by: jimmyl <70376633+mc-oofert@ users.noreply.github.com>

code/modules/reagents/reagent_containers/misc.dm

@@ -91,7 +91,6 @@
 
 /obj/item/reagent_containers/cup/maunamug/attack_hand(mob/living/user, list/modifiers)
 	if(cell && open)
-		cell.update_appearance()
 		user.put_in_hands(cell)
 		cell = null
 		to_chat(user, span_notice("You remove the power cell from [src]."))