[MM-21020] Return same error when creating a duplicate channel (#13429)

* Return same error when trying to create a channel with the same name of an existing one

* Remove unused arguments

store/sqlstore/channel_store.go

@@ -575,9 +575,6 @@ func (s SqlChannelStore) saveChannelT(transaction *gorp.Transaction, channel *mo
 		if IsUniqueConstraintError(err, []string{"Name", "channels_name_teamid_key"}) {
 			dupChannel := model.Channel{}
 			s.GetMaster().SelectOne(&dupChannel, "SELECT * FROM Channels WHERE TeamId = :TeamId AND Name = :Name", map[string]interface{}{"TeamId": channel.TeamId, "Name": channel.Name})
-			if dupChannel.DeleteAt > 0 {
-				return nil, model.NewAppError("SqlChannelStore.Save", "store.sql_channel.save_channel.previously.app_error", nil, "id="+channel.Id+", "+err.Error(), http.StatusBadRequest)
-			}
 			return &dupChannel, model.NewAppError("SqlChannelStore.Save", store.CHANNEL_EXISTS_ERROR, nil, "id="+channel.Id+", "+err.Error(), http.StatusBadRequest)
 		}
 		return nil, model.NewAppError("SqlChannelStore.Save", "store.sql_channel.save_channel.save.app_error", nil, "id="+channel.Id+", "+err.Error(), http.StatusInternalServerError)