Remove perseus-env - no longer used by anything in Perseus

[jeremywiebe]

Summary:

This file (and the symbols it exports/attached to window) are no longer used anywhere in Perseus. Removing to clean thingsup.

Issue: "none"

Test plan:

yarn flow
yarn test
rg KhanUtil - 0 results
rg getCurrentFramework - 0 results
etc

[changeset-bot]

⚠️ No Changeset found

Latest commit: 1df3b05

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

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[github-actions]

Size Change: -17 B (0%)

Total Size: 708 kB

Filename	Size	Change
packages/perseus/dist/es/index.js	418 kB	-17 B (0%)

ℹ️ View Unchanged

Filename	Size
packages/kas/dist/es/index.js	38.4 kB
packages/kmath/dist/es/index.js	4.18 kB
packages/math-input/dist/es/index.js	60 kB
packages/perseus-editor/dist/es/index.js	150 kB
packages/perseus-error/dist/es/index.js	825 B
packages/perseus-linter/dist/es/index.js	19.3 kB
packages/pure-markdown/dist/es/index.js	3.74 kB
packages/simple-markdown/dist/es/index.js	12.9 kB

_{compressed-size-action}

[codecov]

Codecov Report

Merging #275 (1df3b05) into main (988726b) will increase coverage by 3.60%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #275      +/-   ##
==========================================
+ Coverage   47.55%   51.16%   +3.60%     
==========================================
  Files         537      541       +4     
  Lines       29290    32423    +3133     
  Branches     6477     7376     +899     
==========================================
+ Hits        13930    16588    +2658     
- Misses      15360    15835     +475     

Impacted Files	Coverage Δ
packages/perseus/src/util/math.js	30.06% <ø> (+0.69%)	⬆️
testing/test-dependencies.js	32.14% <0.00%> (ø)
vendor/raphael/raphael.js	34.36% <0.00%> (ø)
testing/test-tex.jsx	88.23% <0.00%> (ø)
testing/render-question-with-cypress.jsx	95.45% <0.00%> (ø)
vendor/hubble/hubble.js	36.84% <0.00%> (ø)
packages/perseus/src/util.js	56.91% <0.00%> (+0.32%)	⬆️
...erseus/src/interactive2/movable-polygon-options.js	58.59% <0.00%> (+0.78%)	⬆️
packages/perseus/src/util/tex.js	40.50% <0.00%> (+1.26%)	⬆️
... and 25 more

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