[Glitch] Fix content warning being unnecessarily cleared when enabling/disabling CW

Port 41ca3cdb37 to glitch-soc

Signed-off-by: Thibaut Girka <thib@sitedethib.com>

app/javascript/flavours/glitch/reducers/compose.js

@@ -344,7 +344,6 @@ export default function compose(state = initialState, action) {
     });
   case COMPOSE_SPOILERNESS_CHANGE:
     return state.withMutations(map => {
-      map.set('spoiler_text', '');
       map.set('spoiler', !state.get('spoiler'));
       map.set('idempotencyKey', uuid());