re: 80s Intercom System Removal?

Just a guess, but I would imagine your intercom power transformer is fed from the same circuit as your central ac/heat unit. If the transformer location is known trace the power wire back to a junction box and disconnect it there. (safety disclaimer - disconnect power first and wait until November to do this, unless you love to sweat)

You can leave the antenna wiring as well as the low voltage wiring in the walls/attic.