cvat_sdk.auto_annotation.functions: don't declare useless "N/A" labels

[SpecLad]

Motivation and context

"N/A" is how torchvision marks the gaps in the COCO label list. Since these "labels" should never be output by the models, we should avoid declaring them.

How has this been tested?

Manual testing.

Checklist

• I submit my changes into the develop branch
• I have created a changelog fragment
• [ ] I have updated the documentation accordingly
• [ ] I have added tests to cover my changes
• [ ] I have linked related issues (see GitHub docs)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.39%. Comparing base (eb2fe04) to head (c33481a).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8997   +/-   ##
========================================
  Coverage    73.39%   73.39%           
========================================
  Files          415      415           
  Lines        44184    44184           
  Branches      3859     3859           
========================================
+ Hits         32427    32431    +4     
+ Misses       11757    11753    -4     

Components	Coverage Δ
cvat-ui	77.38% <ø> (+0.01%)	⬆️
cvat-server	70.08% <ø> (ø)