revisit deprecation of is_multiclass

[Borda]

Before submitting

• Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

the is_multiclass was never released so no need for deprecation
on the other hand multilabel was not properly deprecated

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

[codecov]

Codecov Report

Merging #193 (9f05ee8) into master (e0f844c) will increase coverage by 0.77%.
The diff coverage is 94.73%.

@@            Coverage Diff             @@
##           master     #193      +/-   ##
==========================================
+ Coverage   95.98%   96.75%   +0.77%     
==========================================
  Files         180      180              
  Lines        5774     5728      -46     
==========================================
  Hits         5542     5542              
+ Misses        232      186      -46     

Flag	Coverage Δ
Linux	79.95% <94.73%> (+0.63%)	⬆️
Windows	79.95% <94.73%> (+0.63%)	⬆️
cpu	96.75% <94.73%> (+0.77%)	⬆️
gpu	96.75% <ø> (+0.77%)	⬆️
macOS	96.75% <94.73%> (+0.77%)	⬆️
pytest	96.75% <94.73%> (+0.77%)	⬆️
python3.6	95.65% <94.73%> (+0.76%)	⬆️
python3.8	96.71% <94.73%> (+0.77%)	⬆️
python3.9	96.61% <94.73%> (?)
torch1.3.1	95.65% <94.73%> (+0.76%)	⬆️
torch1.4.0	95.77% <94.73%> (+0.76%)	⬆️
torch1.8.1	96.61% <94.73%> (+0.76%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
torchmetrics/classification/stat_scores.py	100.00% <ø> (+2.40%)	⬆️
...chmetrics/functional/classification/stat_scores.py	100.00% <ø> (+6.15%)	⬆️
torchmetrics/utilities/__init__.py	88.88% <83.33%> (-11.12%)	⬇️
torchmetrics/classification/f_beta.py	100.00% <100.00%> (+15.38%)	⬆️
torchmetrics/classification/precision_recall.py	100.00% <100.00%> (+12.50%)	⬆️
torchmetrics/functional/classification/f_beta.py	100.00% <100.00%> (+8.00%)	⬆️
...rics/functional/classification/precision_recall.py	100.00% <100.00%> (+9.52%)	⬆️
__w/2/s/torchmetrics/utilities/__init__.py	88.88% <0.00%> (-11.12%)	⬇️
__w/2/s/torchmetrics/classification/stat_scores.py	100.00% <0.00%> (+2.40%)	⬆️
...chmetrics/functional/classification/stat_scores.py	100.00% <0.00%> (+6.15%)	⬆️
... and 4 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e0f844c...9f05ee8. Read the comment docs.