Figure out if Cljsjs test environments should be removed or replaced

[Deraen]

React 19 no longer provides UMD modules: https://react.dev/blog/2024/04/25/react-19-upgrade-guide#umd-builds-removed

This means there is likely not going to be Cljsjs package for React 19. Reagent no longer has a default dependency on Cljsjs packages, but they are used running the test-suite against Cljsjs version also.

Not sure if test-environments make any sense as the whole cljsjs is pretty much deprecated now. Not sure if a some other test enviornment, like one using esm.sh, would make sense.

[Deraen]

CI jobs for cljsjs have been disabled, but I didn't remove the test setup yet.