Fix migration rollbacks

database/migrations/2019_08_21_104727_add_index_to_beatmapset_events.php

···
     public function down()
     {
         Schema::table('beatmapset_events', function (Blueprint $table) {
-            $table->dropIndex('user_id');
+            $table->dropIndex(['user_id']);
         });
     }
 }

database/migrations/2020_05_15_083037_sync_structure.php

···
      */
     public function down()
     {
-        // no going back =)
+        throw new Exception('no rolling back from this migration =)');
     }
 }

database/migrations/2020_07_22_045416_add_timestamp_index_to_user_account_history.php

···
      */
     public function down()
     {
-        Schema::table('user_account_history', function (Blueprint $table) {
+        Schema::table('osu_user_banhistory', function (Blueprint $table) {
             $table->dropIndex(['timestamp']);
         });
     }

database/migrations/2020_10_13_064901_add_provider_reference_to_orders.php

···
      */
     public function down()
     {
-        Schema::connection('mysql-store')('orders', function (Blueprint $table) {
+        Schema::connection('mysql-store')->table('orders', function (Blueprint $table) {
             $table->dropColumn('provider');
             $table->dropColumn('reference');
-            $table->dropIndex(['provider', 'reference']);
         });
     }
 }

database/migrations/2021_08_30_153214_add_track_id_to_beatmapsets.php

···
     {
         Schema::table('osu_beatmapsets', function (Blueprint $table) {
             $table->dropColumn('track_id');
-            $table->dropIndex('track_id');
         });
     }
 }