Removes checks for bank_hash_stats in test

[brooksprumo]

Problem

AccountsDb::bank_hash_stats is a map of Slot -> BankHashStats. These stats are somewhat special, in that a default value is inserted into the map whenever a new bank is created (from parent). We also have a redundant insert-default whenever store() is called. And lastly new AccountsDb's will insert a default value at slot 0 too. This pre-usage insert-default-value behavior has one potential use: logging an error if a new bank was created with the same slot as a pre-existing one. To check for that case, bank_hash_stats is consulted. This case can happen in unusual forking, and is present in the local-cluster test_optimistic_confirmation_violation_detection test.

Looking up the bank_hash_stats is used in test_handle_dropped_roots_for_ancient() as a way to check if the slot is present or not. The test has other checks to see if the root is dropped, and the bank_hash_stats is not needed here. By using bank_hash_stats, it prevents removing the pre-usage insert-default-value behavior.

(The longer story is that these stats are also stored in snapshots, even though they aren't even used/needed, and I'd like to remove them there also. Incremental changes though!)

Summary of Changes

Remove the calls to get_bank_hash_stats() inside test_handle_dropped_roots_for_ancient(), which already has other way to assert its invariants.

[jeffwashington]

lgtm