[bug] Clear small noms should emit events and/or return stake removed

[camfairchild]

I found a very minor, but annoying bug in the runtime. My beloved coworker unstaked all but 1 rao (X), and now the runtime decided to unstake the full amount (X+1), leading to an additional balances.Deposit of 1 rao, but the SubtensorModule.StakeRemoved event does not include the additional 1 rao, i.e. it reports a removal of X instead of X+1.

I think this is a bug. pallets/subtensor/src/staking/helpers.rs:clear_small_nomination_if_required() should either emit StakeRemoved if it removes stake, or it should return the additional rao removed so that pallets/subtensor/src/staking/remove_stake.rs:do_remove_stake() knows what additional amount to report as being unstaked.

Another way to look at it: Self::deposit_event(Event::StakeRemoved(hotkey, stake_to_be_removed)); should not report "stake to be removed" but "stake actually removed" if these numbers are not equal in practice.

I suspect an additional (minor) bug is that StakeDeltaSinceLastEmissionDrain is not mutated with the correct amount, for the same reason.