netfilter: conntrack: remove CONFIG_NF_CONNTRACK checks from nf_conntrack_zones.h.

nf_conntrack_zones.h was wrapped in a CONFIG_NF_CONNTRACK check in order
to fix compilation failures:

  37ee3d5b ("netfilter: nf_defrag_ipv4: fix compilation error with NF_CONNTRACK=n")

Subsequent changes mean that these failures will no longer occur and the
check is unnecessary.  Remove it.
Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_conntrack_zones.h

@@ -3,9 +3,6 @@
 #define _NF_CONNTRACK_ZONES_H
 
 #include <linux/netfilter/nf_conntrack_zones_common.h>
-
-#if IS_ENABLED(CONFIG_NF_CONNTRACK)
-
 #include <net/netfilter/nf_conntrack.h>
 
 static inline const struct nf_conntrack_zone *
@@ -88,5 +85,5 @@ static inline bool nf_ct_zone_equal_any(const struct nf_conn *a,
 	return true;
 #endif
 }
-#endif /* IS_ENABLED(CONFIG_NF_CONNTRACK) */
+
 #endif /* _NF_CONNTRACK_ZONES_H */