[REVIEW] Remove check_cupy8

[viclafargue]

Closes #3651

[JohnZed]

Looks from the CI failures that there are a few more cases to remove.

[codecov-io]

Codecov Report

Merging #3669 (f2a884b) into branch-0.19 (fd9ec89) will increase coverage by 1.51%.
The diff coverage is 91.14%.

@@               Coverage Diff               @@
##           branch-0.19    #3669      +/-   ##
===============================================
+ Coverage        80.70%   82.22%   +1.51%     
===============================================
  Files              227      226       -1     
  Lines            17615    17454     -161     
===============================================
+ Hits             14217    14352     +135     
+ Misses            3398     3102     -296     

Flag	Coverage Δ
dask	46.48% <32.00%> (+1.48%)	⬆️
non-dask	74.15% <76.28%> (+1.23%)	⬆️

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

Impacted Files	Coverage Δ
...cuml/_thirdparty/sklearn/preprocessing/__init__.py	100.00% <ø> (ø)
python/cuml/cluster/kmeans.pyx	91.95% <ø> (ø)
python/cuml/common/import_utils.py	57.30% <ø> (-1.75%)	⬇️
python/cuml/fil/fil.pyx	92.85% <ø> (+1.02%)	⬆️
python/cuml/model_selection/_split.py	90.86% <ø> (+0.50%)	⬆️
python/cuml/neighbors/__init__.py	100.00% <ø> (ø)
python/cuml/neighbors/ann.pyx	90.80% <ø> (+29.17%)	⬆️
python/cuml/neighbors/nearest_neighbors.pyx	92.97% <ø> (+0.33%)	⬆️
python/cuml/pipeline/__init__.py	100.00% <ø> (ø)
python/cuml/preprocessing/encoders.py	95.10% <ø> (+0.02%)	⬆️
... and 79 more

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[dantegd]

rerun tests

[dantegd]

@gpucibot merge