Minor changes to prepare for Param 2.0

[maximlt]

This PR fixes calls to Param's main warning, as in Param 2.0 the warning method is going to be removed from the Parameterized namespace and will only be available in the .param namespace.

This PR also removes an unused kwarg passed in a test to the HoloViews pane, spotted by Simon in holoviz/param#729.

[codecov]

Codecov Report

Merging #4757 (7dc9637) into main (5ec6ae6) will not change coverage.
The diff coverage is 28.57%.

@@           Coverage Diff           @@
##             main    #4757   +/-   ##
=======================================
  Coverage   73.21%   73.21%           
=======================================
  Files         268      268           
  Lines       37689    37689           
=======================================
  Hits        27595    27595           
  Misses      10094    10094           

Flag	Coverage Δ
unitexamples-tests	73.21% <28.57%> (ø)

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

Impacted Files	Coverage Δ
panel/interact.py	74.30% <0.00%> (ø)
panel/io/embed.py	87.33% <0.00%> (ø)
panel/io/ipywidget.py	0.00% <0.00%> (ø)
panel/io/rest.py	31.63% <0.00%> (ø)
panel/param.py	86.61% <100.00%> (ø)
panel/tests/pane/test_holoviews.py	99.17% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[philippjfr]

Looks good, thanks!