unix: remove pim sysctl/headers from mksysctl_openbsd.go

PIM support was removed from OpenBSD in 2016 and as such, the referenced headers
and sysctl names no longer exist.

Change-Id: I7f3e63741b0d4acb8a43e3615b86381f8071e836
Reviewed-on: https://go-review.googlesource.com/c/sys/+/249618
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

unix/mksysctl_openbsd.go

@@ -163,12 +163,10 @@ func main() {
 		`netinet/ip_gre.h`,
 		`netinet/ip_ipcomp.h`,
 		`netinet/ip_ipip.h`,
-		`netinet/pim_var.h`,
 		`netinet/tcp_var.h`,
 		`netinet/udp_var.h`,
 		`netinet6/in6.h`,
 		`netinet6/ip6_divert.h`,
-		`netinet6/pim6_var.h`,
 		`netinet/icmp6.h`,
 		`netmpls/mpls.h`,
 	}
@@ -211,14 +209,12 @@ func main() {
 		`net.inet.ipip`,
 		`net.inet.mobileip`,
 		`net.inet.pfsync`,
-		`net.inet.pim`,
 		`net.inet.tcp`,
 		`net.inet.udp`,
 		`net.inet6`,
 		`net.inet6.divert`,
 		`net.inet6.ip6`,
 		`net.inet6.icmp6`,
-		`net.inet6.pim6`,
 		`net.inet6.tcp6`,
 		`net.inet6.udp6`,
 		`net.mpls`,