> * if the package includes *precompiled* gschema... remove it?
No, because these don't exist (at least I don't think so). All
installed gschemas are compiled at once based on the schemas installed
on the system, and there are no precompiled schemas.
A few of packages' sources include a gschemas.compiled file.
$ file schemas/gschemas.compiled
schemas/gschemas.compiled: GVariant Database file, version 0