Migrate "Channel.PermanentDeleteMembersByUser" to Sync by default (#11243)

* Change PermanentDeleteMembersByUser to sync by default

* Address comments

store/sqlstore/channel_store.go

@@ -1717,12 +1717,11 @@ func (s SqlChannelStore) RemoveAllDeactivatedMembers(channelId string) *model.Ap
 	return nil
 }
 
-func (s SqlChannelStore) PermanentDeleteMembersByUser(userId string) store.StoreChannel {
-	return store.Do(func(result *store.StoreResult) {
-		if _, err := s.GetMaster().Exec("DELETE FROM ChannelMembers WHERE UserId = :UserId", map[string]interface{}{"UserId": userId}); err != nil {
-			result.Err = model.NewAppError("SqlChannelStore.RemoveMember", "store.sql_channel.permanent_delete_members_by_user.app_error", nil, "user_id="+userId+", "+err.Error(), http.StatusInternalServerError)
-		}
-	})
+func (s SqlChannelStore) PermanentDeleteMembersByUser(userId string) *model.AppError {
+	if _, err := s.GetMaster().Exec("DELETE FROM ChannelMembers WHERE UserId = :UserId", map[string]interface{}{"UserId": userId}); err != nil {
+		return model.NewAppError("SqlChannelStore.RemoveMember", "store.sql_channel.permanent_delete_members_by_user.app_error", nil, "user_id="+userId+", "+err.Error(), http.StatusInternalServerError)
+	}
+	return nil
 }
 
 func (s SqlChannelStore) UpdateLastViewedAt(channelIds []string, userId string) (map[string]int64, *model.AppError) {