removing a publisher: solaris is a system publisher and cannot be unset

Solaris 11.4 zone

I managed to add the Oracle publisher inside the zone. The zone itself is installed in a LDOM, and normally it looks like

[2020-06-26 15:32:00] root@ls-sol-sff98d1:~ # pkg publisher

PUBLISHER                   TYPE     STATUS P LOCATION

solaris        (syspub)     origin   online T <system-repository>

solarisstudio  (syspub)     origin   online T <system-repository>

then I added the Oracle publisher, didn't know that this can happen inside a zone, but hey - why not trying it out?

[2020-06-26 13:36:59] root@ls-sol-sff98d1:~ # pkg set-publisher -k /export/home/labuser/pkg.oracle.com.key_fritz.kraus_dynatrace.com.pem -c /export/home/labuser/pkg.oracle.com.certificate_fritz.kraus_dynatrace.com.pem -G '*' -M '*' -g