refactor: Remove logic and style that accommodates non-flex fallbacks

[roman-bc-dev]

Description

This is a duplicate PR with changes based off of the next branch, instead of main, to avoid pulling updates from 7.20.1.

Remove logic that checks for browser flexbox feature support and any style rules that specifically target the .vjs-no-flex class. We are assuming standard flex support for Video.js 8 and onward.

Specific Changes proposed

• Remove flexNotSupported_() and associated call.
• Remove specific style rules that target the .vjs-no-flex class added by the flexNotSupported_()method. Consolidate css rule groups where .vjs-no-flex targeting was removed.

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Change has been verified in an actual browser (Chrome, Firefox, IE)
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors

[codecov]

Codecov Report

Merging #7820 (c22f057) into next (4cdb2ab) will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             next    #7820      +/-   ##
==========================================
+ Coverage   81.60%   81.65%   +0.04%     
==========================================
  Files         110      110              
  Lines        7350     7341       -9     
  Branches     1777     1771       -6     
==========================================
- Hits         5998     5994       -4     
+ Misses       1352     1347       -5     

Impacted Files	Coverage Δ
src/js/player.js	89.08% <ø> (+0.26%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4cdb2ab...c22f057. Read the comment docs.