Remove glitch-soc's old onboarding modal

app/javascript/flavours/glitch/features/ui/util/async-components.js

@@ -118,10 +118,6 @@ export function Mutes () {
   return import(/* webpackChunkName: "flavours/glitch/async/mutes" */'flavours/glitch/features/mutes');
 }
 
-export function OnboardingModal () {
-  return import(/* webpackChunkName: "flavours/glitch/async/onboarding_modal" */'flavours/glitch/features/ui/components/onboarding_modal');
-}
-
 export function MuteModal () {
   return import(/* webpackChunkName: "flavours/glitch/async/mute_modal" */'flavours/glitch/features/ui/components/mute_modal');
 }