Replaces ReadAccountMapEntry in slots_by_pubkey()

[brooksprumo]

Problem

See #34786 for background.

We want to limit the use of ReadAccountMapEntry, from AccountsIndex, everywhere. Ultimately removing it once there are no more uses.

Bank tests uses AccountsIndex::get(), which calls AccountsIndex::get_account_read_entry(). The slots_by_pubkey() function returns the slots from an entry's slot list as a Vec. We can do the same thing with get_and_then(), instead of get().

Summary of Changes

• Uses get_and_then() in slots_by_pubkey()
• removes unused Ancestors parameter

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (4b65cc8) 81.6% compared to head (aa0f2cb) 81.6%.
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #35241     +/-   ##
=========================================
- Coverage    81.6%    81.6%   -0.1%     
=========================================
  Files         833      833             
  Lines      224765   224770      +5     
=========================================
- Hits       183480   183467     -13     
- Misses      41285    41303     +18     

[HaoranYi]

lgtm