Heal Bell isn't necessarily needed, but on this set, it would be a good choice to keep it.
Heal Bell is helpful when getting rid of Status-conditions; for example, Physical Sweepers hate Burns (unless if guts) because it lowers their Attack, while Walls generally hate badly-Poisoned statuses because it limits their walling capabilities.
Note that it affects the whole team as well, so having Heal Bell would be a good choice on Blissey (it can make it a useful cleric).