Drop last GConf remnants
    
    Commit 9d76a8d dropped the GConf2-devel build dep, but left in the
    %gconf_schema_remove macro in the %preun script, which then no longer
    got expanded and led to rpm script errors during package updates:
    
    /var/tmp/rpm-tmp.t79zGT: line 1: fg: no job control
    
    This drops the macro as well.