[Discuss]feat/refactor account delta for app

[ChefSnoopy]

Remove parameter app from _accountDeltaForApp , will save some gas. Not much , only 10 ~ 20 , just leave here for reference

[chefburger]

i don't have strong opinion on this, it does save gas and relatively risk free.

@chefburger any thoughts?

lgtm as well, dont see any drawback

[chefburger]

btw @ChefSnoopy , before u merge can you also remove PoolKey from IVault. It seems now Vault can be PoolKey agnostic 👏