Refactor remove_uncleaned_slots to reduce memory consumption

[dmakarov]

Problem

Cleaning algorithm creates many temporary data sets that consume significant amount of heap, increasing memory requirements of the validator.

Summary of Changes

Avoid making another temporary container of pubkeys that are candidates for cleaning.

This change reduces the used heap memory by 14% on a sample snapshot cleaning from 166,737,546,218 to 143,515,886,322 bytes.

Also collapse two small functions where the first is the only caller of the second into a single function, and remove a unit test that is almost a duplicate of another existing test that exercises the first of the functions.

[brooksprumo]

The removed_pubkeys here is an owned vec of Pubkeys, right? And it looks like insert_pubkey() take a &Pubkey. So we end up having to make a copy of each pubkey inside insert_pubkey(), even though we might not need to.

If insert_pubkey() took the pubkey by value, I think that would allow us to do something like

for removed_pubkey in removed_pubkeys {
    self.insert_pubkey(candidates, pubkey);
}

To avoid the copy.

And since inside insert_pubkey() we always copy, this seems like an improvement to me. The callers that only have a &Pubkey now explicitly do the copy themselves.

[dmakarov]

I made this change. Thank you.

[brooksprumo]

here:

Suggested change

	fn insert_pubkey(&self, candidates: &[RwLock<HashMap<Pubkey, CleaningInfo>>], pubkey: &Pubkey) {
	let index = self.accounts_index.bin_calculator.bin_from_pubkey(pubkey);
	let mut candidates_bin = candidates[index].write().unwrap();
	candidates_bin.insert(*pubkey, CleaningInfo::default());
	}
	fn insert_pubkey(&self, candidates: &[RwLock<HashMap<Pubkey, CleaningInfo>>], pubkey: Pubkey) {
	let index = self.accounts_index.bin_calculator.bin_from_pubkey(&pubkey);
	let mut candidates_bin = candidates[index].write().unwrap();
	candidates_bin.insert(pubkey, CleaningInfo::default());
	}

[dmakarov]

Done. Thanks.