chore: drop some obsolete dev dependencies (package.json)

[st3iny]

• @typescript-eslint/*: Not required as we use the lint config from @nextcloud/eslint-config.
• @types/webpack-env: We don't even use webpack-env.

To address #7290

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 13.67%. Comparing base (b64f0e6) to head (c6bdc44).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7320   +/-   ##
=======================================
  Coverage   13.67%   13.67%           
=======================================
  Files         218      218           
  Lines       11180    11180           
  Branches     2703     2690   -13     
=======================================
  Hits         1529     1529           
  Misses       9301     9301           
  Partials      350      350           

Flag	Coverage Δ
javascript	13.67% <ø> (ø)

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