Revert "Implement Series.datetime.floor"

[galipremsagar]

Reverts #9488

This PR needs more cpp reviews, hence reverting.

[codecov]

Codecov Report

Merging #9560 (9137de9) into branch-21.12 (ab4bfaa) will decrease coverage by 0.11%.
The diff coverage is n/a.

❗ Current head 9137de9 differs from pull request most recent head 1511cc7. Consider uploading reports for the commit 1511cc7 to get more accurate results

@@               Coverage Diff                @@
##           branch-21.12    #9560      +/-   ##
================================================
- Coverage         10.79%   10.67%   -0.12%     
================================================
  Files               116      117       +1     
  Lines             18869    19718     +849     
================================================
+ Hits               2036     2104      +68     
- Misses            16833    17614     +781     

Impacted Files	Coverage Δ
python/dask_cudf/dask_cudf/sorting.py	92.90% <0.00%> (-1.21%)	⬇️
python/cudf/cudf/io/csv.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/__init__.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)
python/cudf/cudf/core/frame.py	0.00% <0.00%> (ø)
... and 68 more

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