[REVIEW] use the CUB submodule in Thrust instead of fetching it

[rongou]

As suggested in rapidsai/rmm#538.

@harrism @kkraus14

[GPUtester]

Can one of the admins verify this patch?

[GPUtester]

Please update the changelog in order to start CI tests.

View the gpuCI docs here.

[codecov]

Codecov Report

Merging #6155 into branch-0.16 will increase coverage by 0.32%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           branch-0.16    #6155      +/-   ##
===============================================
+ Coverage        84.20%   84.53%   +0.32%     
===============================================
  Files               82       82              
  Lines            13575    13916     +341     
===============================================
+ Hits             11431    11764     +333     
- Misses            2144     2152       +8     

Impacted Files	Coverage Δ
python/cudf/cudf/io/feather.py	100.00% <0.00%> (ø)
python/cudf/cudf/comm/serialize.py	0.00% <0.00%> (ø)
python/custreamz/custreamz/_version.py	0.00% <0.00%> (ø)
python/dask_cudf/dask_cudf/_version.py	0.00% <0.00%> (ø)
python/dask_cudf/dask_cudf/io/tests/test_orc.py	100.00% <0.00%> (ø)
python/dask_cudf/dask_cudf/io/tests/test_json.py	100.00% <0.00%> (ø)
...ython/custreamz/custreamz/tests/test_dataframes.py	100.00% <0.00%> (ø)
...ython/dask_cudf/dask_cudf/io/tests/test_parquet.py	100.00% <0.00%> (ø)
python/cudf/cudf/utils/applyutils.py	98.75% <0.00%> (+0.02%)	⬆️
python/cudf/cudf/core/join/join.py	92.41% <0.00%> (+0.03%)	⬆️
... and 30 more

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[kkraus14]

rerun tests