Remove pkg/systemd from validate-lint

Following #15330, pkg/systemd doesn't exists anymore.

Signed-off-by: Vincent Demeester <vincent@sbr.pm>

hack/make/validate-lint

@@ -74,7 +74,6 @@ packages=(
 	pkg/stringid
 	pkg/stringutils
 	pkg/sysinfo
-	pkg/systemd
 	pkg/symlink
 	pkg/tailfile
 	pkg/tarsum