Did you also create a Routing Group Connector between two Exchange systems with the -BiDirectional parameter of the new-routinggroupconnector cmdlet? When you try to remove the Routing Group Connector you receive the following error:

Remove-RoutingGroupConnector : The operation could not be performed because ‘le
gacy routing group connector’ matches multiple entries.
At line:1 char:29

Just remove the Routing Group Connectors with the following command;

get-routinggroupconnector -Identity “legacy routing group connector” |R

If you want to delete all the connectors, just leave out the identity parameter.