Replaces fs-err in verify_snapshot_archive()

[brooksprumo]

Problem

We're trying to remove the fs-err crate. For more information, please refer to #34838.

Some uses of fs-err in snapshot_utils.rs can easily be replaced with their std::fs counterparts.

Summary of Changes

Replace 'em. Note that all these uses are in a DCOU fn, so test-only.

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (f9bfb60) 81.7% compared to head (03f0006) 81.7%.
Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #34887     +/-   ##
=========================================
- Coverage    81.7%    81.7%   -0.1%     
=========================================
  Files         826      826             
  Lines      223371   223383     +12     
=========================================
- Hits       182578   182567     -11     
- Misses      40793    40816     +23