[REVIEW] Fix __repr__ for categorical dtype

[galipremsagar]

Fixes: #7470

This PR:

• Handles the dtype/categories representation correctly in a sliced series/Index.
• Removes some NumPy deprecated code usages.

[kkraus14]

@gpucibot merge

[galipremsagar]

rerun tests

[codecov]

Codecov Report

Merging #7476 (30ca48a) into branch-0.19 (f79a841) will increase coverage by 0.39%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           branch-0.19    #7476      +/-   ##
===============================================
+ Coverage        81.86%   82.26%   +0.39%     
===============================================
  Files              101      101              
  Lines            16883    17244     +361     
===============================================
+ Hits             13821    14185     +364     
+ Misses            3062     3059       -3     

Impacted Files	Coverage Δ
python/cudf/cudf/core/index.py	93.34% <ø> (+0.48%)	⬆️
python/cudf/cudf/core/series.py	91.12% <ø> (+0.34%)	⬆️
python/cudf/cudf/core/dataframe.py	90.58% <100.00%> (+0.12%)	⬆️
python/cudf/cudf/core/frame.py	89.12% <100.00%> (+0.10%)	⬆️
python/cudf/cudf/core/indexing.py	96.11% <100.00%> (+0.05%)	⬆️
python/cudf/cudf/core/scalar.py	87.43% <100.00%> (+0.33%)	⬆️
python/cudf/cudf/utils/utils.py	85.71% <100.00%> (+0.28%)	⬆️
python/cudf/cudf/utils/gpu_utils.py	53.65% <0.00%> (-4.88%)	⬇️
python/cudf/cudf/core/abc.py	87.23% <0.00%> (-1.14%)	⬇️
python/cudf/cudf/io/feather.py	100.00% <0.00%> (ø)
... and 47 more

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[kkraus14]

rerun tests