Don't emit a warning when data has timezone in it

[hoxbro]

Saw this warning in a hvplot notebook:

/home/shh/Repos/holoviz/holoviews/holoviews/core/data/pandas.py:364: FutureWarning: The behavior of DatetimeProperties.to_pydatetime is deprecated, in a future version this will return a Series containing python datetime objects instead of an ndarray. To retain the old behavior, call `np.array` on the result
  dts = [dt.replace(tzinfo=None) for dt in data.dt.to_pydatetime()]

This means that our test did not go down this code path. The fix was simple as I simply used a pandas built-in approach of removing timezone. This also has the advantage that we are not rounding our data to microseconds and also using a vectorized approach.

Added a small test to go down the code path.

[codecov-commenter]

Codecov Report

Merging #5898 (c0d0c58) into main (63a1cda) will increase coverage by 0.00%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #5898   +/-   ##
=======================================
  Coverage   88.40%   88.41%           
=======================================
  Files         312      312           
  Lines       64943    64948    +5     
=======================================
+ Hits        57412    57422   +10     
+ Misses       7531     7526    -5     

Flag	Coverage Δ
ui-tests	23.33% <14.28%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
holoviews/core/data/pandas.py	94.13% <100.00%> (+0.66%)	⬆️
holoviews/tests/core/data/test_pandasinterface.py	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes

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[github-actions]

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