tcp: do not export tcp_twsk_purge()

After commit 1eeb50435739 ("tcp/dccp: do not care about
families in inet_twsk_purge()") tcp_twsk_purge() is
no longer potentially called from a module.

Signed-off-by: Eric Dumazet <[e-mail]>
Cc: Kuniyuki Iwashima <[e-mail]>
Reviewed-by: Kuniyuki Iwashima <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/tcp_minisocks.c

···
 		}
 	}
 }
-EXPORT_SYMBOL_GPL(tcp_twsk_purge);
 
 /* Warning : This function is called without sk_listener being locked.
  * Be sure to read socket fields once, as their value could change under us.