Fixed usage of old param API in util

[jlstevens]

Discovered while trying to update param API usage in holoviz/holoviews#4201. There may be others so don't merge the PR just yet...

[codecov]

Codecov Report

Merging #992 into master will decrease coverage by 0.12%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #992      +/-   ##
==========================================
- Coverage   85.83%   85.71%   -0.13%     
==========================================
  Files          99       99              
  Lines       11260    11260              
==========================================
- Hits         9665     9651      -14     
- Misses       1595     1609      +14

Impacted Files	Coverage Δ
panel/util.py	85.9% <100%> (-3.36%)	⬇️
panel/interact.py	73.57% <0%> (-2.5%)	⬇️
panel/pane/vtk/vtk.py	52.38% <0%> (-1.06%)	⬇️

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[philippjfr]

Thanks.