Remove outdated css file

[jhonatan-lopes]

The problem

When trying to access the "compare revisions" view in a project with DEBUG=False and whitenoise set up, the view gives a 500 error with the following message:

ValueError: Missing staticfiles manifest entry for 'wagtailadmin/css/layouts/compare-revisions.css'

The cause

This issue is caused by the 'wagtailadmin/css/layouts/compare-revisions.css' stylesheet being moved out of the admin app and into a core.css stylesheet on the 4.0.X branch. See:

• https://github.com/wagtail/wagtail/blob/stable/4.0.x/client/scss/core.scss#L190
• https://github.com/wagtail/wagtail/blob/stable/4.0.x/client/scss/layouts/_compare-revisions.scss

The solution

Since core.scss is already loaded by default on the admin panel, the 'compare-revisions.css' stylesheet will also be loaded by default on 4+ versions of Wagtail. Hence, we can simply remove the imports for those stylesheets.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (31909a4) 87.84% compared to head (d46e06a) 87.84%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #66   +/-   ##
=======================================
  Coverage   87.84%   87.84%           
=======================================
  Files          15       15           
  Lines         732      732           
  Branches      137      137           
=======================================
  Hits          643      643           
  Misses         54       54           
  Partials       35       35           

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