tipc: Remove unused declaration tipc_link_build_bc_sync_msg()

Commit 52666986 ("tipc: let broadcast packet reception use new link receive function")
declared but never implemented this.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20230807142926.45752-1-yuehaibing@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>