Use exists query instead of count in clean-duplicate-history command.

[bigtimecriminal]

Description

Instead of using a nested count query in clean-duplicate-history, use exists unless we're at verbose >= 2

Related Issue

#1014

Motivation and Context

Removes costly query that only exists to log something out on a log that might not be called.

How Has This Been Tested?

Ran all tests. Command is already being tested by test suite

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• I have run the pre-commit run command to format and lint.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have added my name and/or github handle to AUTHORS.rst
• I have added my change to CHANGES.rst
• All new and existing tests passed.

[rossmechanic]

lgtm

[codecov]

Codecov Report

Merging #1015 (bf8bfd2) into master (fd9aa52) will decrease coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1015      +/-   ##
==========================================
- Coverage   96.94%   96.87%   -0.08%     
==========================================
  Files          23       23              
  Lines        1277     1278       +1     
  Branches      210      211       +1     
==========================================
  Hits         1238     1238              
  Misses         21       21              
- Partials       18       19       +1     

Files	Coverage Δ
...ory/management/commands/clean_duplicate_history.py	96.05% <100.00%> (-1.29%)	⬇️

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[ddabble]

Looks like this was simply forgotten about, so I'll merge now :)