remove deprecated from v0.4 & fix past

[Borda]

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• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

Fixes #371

PR review

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[codecov]

Codecov Report

Merging #379 (e12c0c8) into master (849a200) will decrease coverage by 0.08%.
The diff coverage is 94.00%.

@@            Coverage Diff             @@
##           master     #379      +/-   ##
==========================================
- Coverage   96.45%   96.36%   -0.09%     
==========================================
  Files         117      118       +1     
  Lines        3720     3719       -1     
==========================================
- Hits         3588     3584       -4     
- Misses        132      135       +3     

Flag	Coverage Δ
Linux	76.68% <92.00%> (-0.07%)	⬇️
Windows	76.68% <92.00%> (-0.07%)	⬇️
cpu	96.31% <94.00%> (-0.09%)	⬇️
gpu	96.28% <94.00%> (-0.09%)	⬇️
macOS	96.31% <94.00%> (-0.09%)	⬇️
pytest	96.36% <94.00%> (-0.09%)	⬇️
python3.6	95.48% <94.00%> (-0.09%)	⬇️
python3.8	95.56% <94.00%> (-0.84%)	⬇️
python3.9	96.20% <94.00%> (-0.09%)	⬇️
torch1.3.1	95.48% <94.00%> (-0.09%)	⬇️
torch1.4.0	95.56% <94.00%> (-0.09%)	⬇️
torch1.9.0	96.20% <94.00%> (-0.09%)	⬇️

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

Impacted Files	Coverage Δ
...hmetrics/classification/binned_precision_recall.py	98.63% <ø> (-1.37%)	⬇️
torchmetrics/functional/regression/r2.py	95.12% <ø> (-0.44%)	⬇️
torchmetrics/regression/r2score.py	71.42% <75.00%> (-22.86%)	⬇️
torchmetrics/regression/r2.py	94.28% <94.28%> (ø)
torchmetrics/functional/__init__.py	100.00% <100.00%> (ø)
torchmetrics/functional/regression/__init__.py	100.00% <100.00%> (ø)
torchmetrics/functional/regression/r2score.py	100.00% <100.00%> (ø)
torchmetrics/regression/__init__.py	100.00% <100.00%> (ø)
... and 1 more

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