tcp/ipv4: remove AF_INET_FAMILY

After commit 079096f103fa ("tcp/dccp: install syn_recv requests into ehash table")
the macro isn't used anymore. remove it.

Signed-off-by: Alex Shi <[e-mail]>
Cc: "David S. Miller" <[e-mail]>
Cc: Alexey Kuznetsov <[e-mail]>
Cc: Hideaki YOSHIFUJI <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/inet_connection_sock.c

···
 }
 EXPORT_SYMBOL_GPL(inet_csk_route_child_sock);
 
-#if IS_ENABLED(CONFIG_IPV6)
-#define AF_INET_FAMILY(fam) ((fam) == AF_INET)
-#else
-#define AF_INET_FAMILY(fam) true
-#endif
-
 /* Decide when to expire the request and when to resend SYN-ACK */
 static inline void syn_ack_recalc(struct request_sock *req, const int thresh,
 				  const int max_retries,