Uses real stored count in check_storage()

[brooksprumo]

Problem

In check_storage(), it uses the approximate store count to get the total number of accounts stored in an append vec. There's already a better dcou fn for getting the total number of accounts: accounts_count().

We can use accounts_count() in check_storage(), and also be explicit about how many alive vs total accounts we expect.

Summary of Changes

Use accounts_count() in check_storage(), and also be explicit about how many alive vs total accounts we expect.

[jeffwashington]

lgtm. just testing