release/tools: use same pkg settings in containers as in /etc/pkg/FreeBSD.conf

Instructions in /etc/pkg/FreeBSD.conf and elsewhere recommend putting
changes in /usr/local/etc/pkg/repos/FreeBSD.conf so bring OCI containers
into line as well.

Reviewed by:	dfr, ivy
Differential Revision:	https://reviews.freebsd.org/D54090

MFC after:	5 days
Sponsored by:	SkunkWerks, GmbH

release/tools/oci-image-static.conf

@@ -36,12 +36,8 @@ oci_image_build() {
 			;;
 	esac
 	mkdir -p $m/usr/local/etc/pkg/repos
-	cat > $m/usr/local/etc/pkg/repos/base.conf <<EOF
+	cat > $m/usr/local/etc/pkg/repos/FreeBSD.conf <<EOF
 FreeBSD-base: {
-  url: "https://pkg.FreeBSD.org/\${ABI}/${repo}",
-  mirror_type: "srv",
-  signature_type: "fingerprints",
-  fingerprints: "/usr/share/keys/pkg",
   enabled: yes
 }
 EOF