Chore (Core App): Remove legacy bootstrap stylesheets

[joshuarrrr]

Description

This will not target main until after much more thorough testing. But for now, I want to remove these legacy stylesheets from the feature branch so we can start discovering the (expectedly rare) cases where they're actually having any effect.

Issues Resolved

Fixes #4305

Screenshot

Testing the changes

Check List

• All tests pass
  • yarn test:jest
  • yarn test:jest_integration
  • yarn test:ftr
• New functionality includes testing.
• New functionality has been documented.
• Update CHANGELOG.md
• Commits are signed per the DCO using --signoff

[codecov]

Codecov Report

Merging #4385 (e66089b) into main (b3104ce) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #4385      +/-   ##
==========================================
+ Coverage   66.74%   66.77%   +0.03%     
==========================================
  Files        3284     3284              
  Lines       63095    63095              
  Branches    10049    10049              
==========================================
+ Hits        42110    42134      +24     
+ Misses      18488    18487       -1     
+ Partials     2497     2474      -23     

Flag	Coverage Δ
Linux_1	35.26% <ø> (ø)
Linux_2	55.24% <ø> (?)
Linux_3	43.84% <ø> (-0.01%)	⬇️
Linux_4	35.36% <ø> (+<0.01%)	⬆️
Windows_1	35.27% <ø> (ø)
Windows_2	55.20% <ø> (ø)
Windows_3	43.85% <ø> (ø)
Windows_4	35.36% <ø> (ø)

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

Files	Coverage Δ
src/legacy/ui/ui_render/ui_render_mixin.js	0.00% <ø> (ø)

... and 20 files with indirect coverage changes

[joshuarrrr]

Closing as this will take more work to do at some point

[ananzh]

@joshuarrrr Due to an extended period without updates, we're going to close this issue for now. We appreciate your contribution and understand that priorities and availability can change. Please feel free to reopen this issue when you have the opportunity to revisit it. Thank you for your understanding.