Remove various unused functions

[vyasr]

This PR removes a number of unused functions and inlines some helpers that are only called in one place. This PR also deprecates Series.fill, which does not appear to be a pandas API. This PR resolves #9824.

[bdice]

I'm reviewing this to help resolve #9824. I see a few inconsistencies with imports, otherwise LGTM.

[bdice]

LGTM!

[bdice]

@vyasr CI is failing for dask-cudf because the removed function _get_numeric_data is called by dask in two places:

• cudf/python/dask_cudf/dask_cudf/core.py

  Line 432 in a4dc42d

  num = ddf._get_numeric_data()

• cudf/python/dask_cudf/dask_cudf/core.py

  Line 479 in a4dc42d

  num = ddf._get_numeric_data()

[vyasr]

• numeric

I saw, just hadn't gotten around to fixing it yet. Will address it later today. Those specific calls aren't the issue, because they're calls to methods of the dask DataFrame objects and dask.dataframe.DataFrame implements the method. The problem is that dask.dataframe.DataFrame.describe assumes that the underlying DataFrame library (in this case, cudf.DataFrame) has the method. So I think we're stuck just leaving the method there as is.

[vyasr]

rerun tests

[bdice]

I merged in branch-22.02 with my fix from #9951 to help make CI pass. This should be mergeable once CI passes.

[codecov]

Codecov Report

Merging #9922 (ea6b3d3) into branch-22.02 (04f4219) will increase coverage by 0.04%.
The diff coverage is 0.00%.

❗ Current head ea6b3d3 differs from pull request most recent head 3637574. Consider uploading reports for the commit 3637574 to get more accurate results

@@               Coverage Diff                @@
##           branch-22.02    #9922      +/-   ##
================================================
+ Coverage         10.37%   10.41%   +0.04%     
================================================
  Files               119      119              
  Lines             20111    20481     +370     
================================================
+ Hits               2086     2134      +48     
- Misses            18025    18347     +322     

Impacted Files	Coverage Δ
python/cudf/cudf/core/dataframe.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/frame.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/series.py	0.00% <0.00%> (ø)
python/cudf/cudf/io/hdf.py	0.00% <0.00%> (ø)
python/cudf/cudf/io/orc.py	0.00% <0.00%> (ø)
python/cudf/cudf/_version.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/abc.py	0.00% <0.00%> (ø)
python/cudf/cudf/api/types.py	0.00% <0.00%> (ø)
python/cudf/cudf/io/dlpack.py	0.00% <0.00%> (ø)
... and 51 more

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[vyasr]

@gpucibot merge