chore: remove unused moduleSchemas and related API endpoint for legacy modules

We didn't reach the state where we would display these schemas in the
UI.
We might need to wire this up in a similar way for the newer
clan.services

lib/build-clan/interface.nix

@@ -158,7 +158,6 @@ in
           # all exported clan modules from this clan
           modules = lib.mkOption { type = lib.types.raw; };
           # all inventory module schemas
-          moduleSchemas = lib.mkOption { type = lib.types.raw; };
           inventoryFile = lib.mkOption { type = lib.types.raw; };
           # The machine 'imports' generated by the inventory per machine
           inventoryClass = lib.mkOption { type = lib.types.raw; };