[REVIEW] remove Single Process Multi GPU (SPMG) code (fixes #2979)

[jameslamb]

This PR attempts to fix #2979 . In #2976 (comment), I was informed that cuml's Single Process Multi GPU (SPMG) code has been deprecated for a while and can be safely removed.

That comment specifically mentioned python/cuml/dask/common/spmg_ipc.py, but I found a few other places that mention SPMG and look like they can safely be removed.

I ran the following commands to search for relevant code:

git grep -i spmg
git grep -E "Single.*Pro"
git ls-files | grep -i spmg
git ls-files | grep -i single

Thanks for your time and consideration.

[GPUtester]

Can one of the admins verify this patch?

[GPUtester]

Can one of the admins verify this patch?

[GPUtester]

Can one of the admins verify this patch?

[JohnZed]

ok to test

[dantegd]

@jameslamb thanks for the PR! Due to timing, this will not make it to branch0.16 but to 0.17, I was wondering if you could change the target branch appropriately? (If you have any doubts how to do it I'm glad to help or do it directly). Thanks!

[codecov-io]

Codecov Report

Merging #3004 into branch-0.17 will increase coverage by 9.95%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           branch-0.17    #3004      +/-   ##
===============================================
+ Coverage        58.87%   68.82%   +9.95%     
===============================================
  Files              143      234      +91     
  Lines             9004    18493    +9489     
===============================================
+ Hits              5301    12728    +7427     
- Misses            3703     5765    +2062     

Impacted Files	Coverage Δ
python/cuml/dask/solvers/cd.py	54.54% <ø> (ø)
python/cuml/test/test_logger.py	100.00% <0.00%> (ø)
python/cuml/test/stemmer_tests/test_stemmer.py	100.00% <0.00%> (ø)
python/cuml/test/test_mbsgd_classifier.py	100.00% <0.00%> (ø)
python/cuml/test/test_make_blobs.py	100.00% <0.00%> (ø)
python/cuml/test/dask/test_serialization.py	0.00% <0.00%> (ø)
python/cuml/test/dask/test_label_binarizer.py	0.00% <0.00%> (ø)
python/cuml/test/test_coordinate_descent.py	100.00% <0.00%> (ø)
python/cuml/test/dask/test_umap.py	0.00% <0.00%> (ø)
python/cuml/test/test_nearest_neighbors.py	97.80% <0.00%> (ø)
... and 83 more

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[jameslamb]

@jameslamb thanks for the PR! Due to timing, this will not make it to branch0.16 but to 0.17, I was wondering if you could change the target branch appropriately? (If you have any doubts how to do it I'm glad to help or do it directly). Thanks!

no problem! I just updated the target branch.

[dantegd]

lgtm, thanks @jameslamb