Remove doc for deprecated function one_hot_encoding

[isVoid]

This PR removes doc item for deprecated function one_hot_encoding.

[bdice]

Caught something after approving. Let's fix the header text to match pandas - we no longer have "encoding" and can match the pandas header name.

[bdice]

Fix the heading underlines and this is good to go! Thanks @isVoid!

[vyasr]

You can merge once @bdice approves.

[isVoid]

@gpucibot merge

[codecov]

Codecov Report

Merging #10367 (9358387) into branch-22.04 (a7d88cd) will increase coverage by 0.15%.
The diff coverage is n/a.

❗ Current head 9358387 differs from pull request most recent head aeae195. Consider uploading reports for the commit aeae195 to get more accurate results

@@               Coverage Diff                @@
##           branch-22.04   #10367      +/-   ##
================================================
+ Coverage         10.42%   10.58%   +0.15%     
================================================
  Files               119      125       +6     
  Lines             20603    21058     +455     
================================================
+ Hits               2148     2228      +80     
- Misses            18455    18830     +375     

Impacted Files	Coverage Δ
...ython/custreamz/custreamz/tests/test_dataframes.py	99.39% <0.00%> (-0.01%)	⬇️
python/cudf/cudf/errors.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/ops.py	0.00% <0.00%> (ø)
python/cudf/cudf/datasets.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/frame.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/index.py	0.00% <0.00%> (ø)
python/cudf/cudf/io/parquet.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/series.py	0.00% <0.00%> (ø)
... and 43 more

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