Remove scss_to_js

Followup from this review note:

we could also remove the usage of scss_to_js in GitLab in the integration branch to use the compiled design token JS constants like import { DATA_VIZ_BLUE_500 } from '@gitlab/ui/dist/tokens/js/tokens'. Can also handle in follow-ups to remove scss_to_js in general.

Proposal

• remove scss_to_js

  • package json scripts
  • directory
  • makefile script

• update GitLab to not use these

  • find usages of scss_to_js and replace with dist/tokens