Discourse has a custom stylesheet pipeline which compiles things 'just in time'. The only place we were still running sass files through sprockets was for the `/tests` route in development mode. This use can be removed by compiling the relevant stylesheets through ember-cli instead (which we were already doing for testem runs)
This work was prompted by the incompatibility of dartsass-sprockets with the latest sass-embedded release (https://github.com/tablecheck/dartsass-sprockets/issues/13)
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