tipc: Remove unused declaration tipc_link_build_bc_sync_msg()

Commit 526669866140 ("tipc: let broadcast packet reception use new link receive function")
declared but never implemented this.

Signed-off-by: Yue Haibing <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/tipc/link.h

···
 			 struct tipc_gap_ack_blks *ga,
 			 struct sk_buff_head *xmitq,
 			 struct sk_buff_head *retrq);
-void tipc_link_build_bc_sync_msg(struct tipc_link *l,
-				 struct sk_buff_head *xmitq);
 void tipc_link_bc_init_rcv(struct tipc_link *l, struct tipc_msg *hdr);
 int tipc_link_bc_sync_rcv(struct tipc_link *l,   struct tipc_msg *hdr,
 			  struct sk_buff_head *xmitq);