Tweak checking icons

[silvenon]

Checking icons implemented in #2332 is awesome, but I missed three requirements when reviewing it:

1. it should not run when required (which is why it runs on postinstall as well), only when run with node
   • this is tricky, I don't know what to do here other than create our own development CLI using a tool like yargs, as a separate private package
2. it should only run in pre-commit and on CI
   • we should remove it from build
   • we should add it to test-ci, probably right at the beginning
3. it should not have output, it's not necessary