chore!: remove /api/server/theme endpoint (#27880)

chore: remove server/theme endpoint

server/src/controllers/server.controller.ts

@@ -11,7 +11,6 @@ import {
   ServerPingResponse,
   ServerStatsResponseDto,
   ServerStorageResponseDto,
-  ServerThemeDto,
   ServerVersionHistoryResponseDto,
   ServerVersionResponseDto,
 } from 'src/dtos/server.dto';
@@ -104,16 +103,6 @@ export class ServerController {
     return this.service.getFeatures();
   }
 
-  @Get('theme')
-  @Endpoint({
-    summary: 'Get theme',
-    description: 'Retrieve the custom CSS, if existent.',
-    history: new HistoryBuilder().added('v1').beta('v1').stable('v2'),
-  })
-  getTheme(): Promise<ServerThemeDto> {
-    return this.service.getTheme();
-  }
-
   @Get('config')
   @Endpoint({
     summary: 'Get config',