Fix hist on overlay

[Hoxbro]

I noticed while looking at docs failures: https://holoviews.org/Homepage.html

I don't think we use this file anymore, so I could delete it. Deleted it.

I need to use a plotting backend or else I will get ValueError: No plotting extension is currently loaded. This is built on top of the changes made in #5954

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6e5eacf) 88.58% compared to head (4ac72cc) 88.60%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5995      +/-   ##
==========================================
+ Coverage   88.58%   88.60%   +0.02%     
==========================================
  Files         315      315              
  Lines       65583    65592       +9     
==========================================
+ Hits        58095    58121      +26     
+ Misses       7488     7471      -17     

Flag	Coverage Δ
ui-tests	23.27% <45.45%> (+<0.01%)	⬆️

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