Replace undefined func
Created by: gspasov
NY-7298 Replace roster_channel_helper:get_channel_by_id/1 with kvs:get/2
This bug came from the fact that there are still calls to the channel implementation that was removed. This is not the only place where we have calls to modules that don't exist in the codebase anymore. There are several other calls that may crash at some point. All other uses of the channel functions should be looked into and see how they might be resolved: deleted or refactored.