chore(dashboard): remove obsolete js widget

[st3iny]

We dropped support for <= 30 so we can drop the old frontend/js widget code.

Also addresses a warning from renovate:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 23.89%. Comparing base (401f674) to head (d97533d).
Report is 3 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6250      +/-   ##
============================================
+ Coverage     23.71%   23.89%   +0.18%     
+ Complexity      457      454       -3     
============================================
  Files           249      246       -3     
  Lines         11765    11651     -114     
  Branches       2211     2199      -12     
============================================
- Hits           2790     2784       -6     
+ Misses         8660     8551     -109     
- Partials        315      316       +1     

Flag	Coverage Δ
javascript	15.46% <ø> (+0.16%)	⬆️
php	59.53% <ø> (-0.01%)	⬇️

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