gs-page: Prevent removing compulsory apps
This makes the following command just open the details page for gnome-software, rather than going ahead and trying to uninstall it:
gnome-software --uninstall=system/package/fedora/org.gnome.Software.desktop/*
Spotted in !1389 (comment 1474003).
Signed-off-by: Philip Withnall pwithnall@endlessos.org