Remove concurrent_unordered_multimap.

[bdice]

The concurrent_unordered_multimap is no longer used in libcudf. It has been replaced by cuco::static_multimap. The majority of the refactoring was done in PRs #8934 and #9704. A similar effort is in progress for concurrent_unordered_map and cuco::static_map in #9666 (and may depend on porting some optimizations from libcudf to cuco -- need to look into this before doing a direct replacement).

This partially resolves issue #10401.

cc: @PointKernel @vyasr

[jrhemstad]

rerun tests

[codecov]

Codecov Report

Merging #10642 (df68de1) into branch-22.06 (3c13ef1) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@               Coverage Diff                @@
##           branch-22.06   #10642      +/-   ##
================================================
+ Coverage         86.33%   86.37%   +0.04%     
================================================
  Files               140      140              
  Lines             22289    22290       +1     
================================================
+ Hits              19244    19254      +10     
+ Misses             3045     3036       -9     

Impacted Files	Coverage Δ
python/cudf/cudf/core/algorithms.py	90.47% <ø> (ø)
python/cudf/cudf/core/dataframe.py	93.59% <ø> (ø)
python/cudf/cudf/core/groupby/groupby.py	91.72% <ø> (+0.22%)	⬆️
python/cudf/cudf/core/multiindex.py	92.14% <ø> (ø)
python/cudf/cudf/core/series.py	95.28% <ø> (ø)
python/cudf/cudf/core/single_column_frame.py	96.45% <ø> (ø)
python/cudf/cudf/utils/cudautils.py	59.83% <ø> (ø)
python/cudf/cudf/utils/ioutils.py	79.60% <ø> (ø)
python/cudf/cudf/utils/utils.py	90.28% <ø> (ø)
python/cudf/cudf/core/column/lists.py	92.79% <100.00%> (+1.38%)	⬆️
... and 6 more

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[bdice]

@gpucibot merge