Remove unused mypy ignores

[jklaise]

Same motivation as SeldonIO/alibi#874

[codecov]

Codecov Report

Merging #794 (310a9ae) into master (0361fbd) will not change coverage.
The diff coverage is 94.82%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #794   +/-   ##
=======================================
  Coverage   81.45%   81.45%           
=======================================
  Files         154      154           
  Lines       10048    10048           
=======================================
  Hits         8185     8185           
  Misses       1863     1863           

Impacted Files	Coverage Δ
alibi_detect/ad/model_distillation.py	91.80% <0.00%> (ø)
alibi_detect/cd/pytorch/lsdd_online.py	95.78% <0.00%> (ø)
alibi_detect/cd/base.py	90.97% <85.71%> (ø)
alibi_detect/base.py	85.45% <100.00%> (ø)
alibi_detect/cd/base_online.py	88.23% <100.00%> (ø)
alibi_detect/cd/chisquare.py	97.14% <100.00%> (ø)
alibi_detect/cd/classifier.py	100.00% <100.00%> (ø)
alibi_detect/cd/context_aware.py	97.43% <100.00%> (ø)
alibi_detect/cd/keops/mmd.py	98.21% <100.00%> (ø)
alibi_detect/cd/learned_kernel.py	100.00% <100.00%> (ø)
... and 23 more