Remove get_num_classes in jaccard_index

[rusty1s]

What does this PR do?

This PR removes the get_num_classes call in jaccard_index. This call is no longer required since the num_classes argument of jaccard_index is now mandatory. Since get_num_classes is not used anywhere else, I removed the function completely.

Before submitting

• Was this discussed/approved via Slack? (discussed with @SkafteNicki and @Borda)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

[codecov]

Codecov Report

Merging #914 (ce147fa) into master (712a81b) will decrease coverage by 0%.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #914   +/-   ##
=====================================
- Coverage      95%    95%   -0%     
=====================================
  Files         173    173           
  Lines        7344   7332   -12     
=====================================
- Hits         6976   6962   -14     
- Misses        368    370    +2     

[Borda]

mind adding a record to changelog? 🐰

[rusty1s]

done :)

[rusty1s]

What's the reason for the failing CI? Anything I can do about it?

[Borda]

What's the reason for the failing CI? Anything I can do about it?

well, atm seems there is some connection error so nothing related to this PR :/