I dont think that you want to stop synchronization for all just because of archiving one material.
Unfortunately I dont have a system like that, but I guess there is a table somewhere which has the link between the material master and the product master, probably the one which is bespoken in this discussion: Name of the material master table in SRM
You should contact your colleague who maintains such catalogs, he probably knows as well how to remove a allocation. Maybe it is as easy like clicking a trash can icon