Small cleanup.

[trivialfis]

• Remove unused code.
• Fix comment.

[cjnolet]

@trivialfis, really happy to see these prims being cleaned up a bit. Some of them haven't been touched much since the original version of UMAP was written back in 2019 and can really use some TLC.

As a side note- the sparse prims have all been moved to RAFT and I've had #3554 open to remove them from cuml and adjust the includes to use the versions from RAFT. Unfortunately, it hasn't been merged yet because it's been waiting on updates to other prims, which I need to update in RAFT again. It would be helpful if any sparse prims changes going forward are made directly in RAFT so that we can get #3554 merged quickly.

[codecov-io]

Codecov Report

Merging #3575 (ad34ffc) into branch-0.19 (9fa6e17) will increase coverage by 35.80%.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           branch-0.19    #3575       +/-   ##
================================================
+ Coverage        44.99%   80.80%   +35.80%     
================================================
  Files              223      227        +4     
  Lines            16921    17735      +814     
================================================
+ Hits              7614    14331     +6717     
+ Misses            9307     3404     -5903     

Flag	Coverage Δ
dask	45.30% <ø> (+0.31%)	⬆️
non-dask	73.06% <ø> (?)

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

Impacted Files	Coverage Δ
python/cuml/dask/solvers/cd.py	100.00% <0.00%> (ø)
python/cuml/common/numba_utils.py	0.00% <0.00%> (ø)
python/cuml/internals/global_settings.py	100.00% <0.00%> (ø)
python/cuml/dask/preprocessing/encoders.py	100.00% <0.00%> (ø)
...n/cuml/experimental/explainer/permutation_shap.pyx	98.82% <0.00%> (ø)
python/cuml/experimental/explainer/base.pyx	67.06% <0.00%> (ø)
python/cuml/experimental/explainer/kernel_shap.pyx	97.75% <0.00%> (ø)
python/cuml/experimental/linear_model/lars.pyx	96.53% <0.00%> (ø)
python/cuml/dask/common/dask_arr_utils.py	95.83% <0.00%> (+0.05%)	⬆️
python/cuml/dask/cluster/dbscan.py	97.29% <0.00%> (+0.07%)	⬆️
... and 129 more

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[trivialfis]

@cjnolet Thanks, let me look into raft tomorrow. Closing this.