tipc: purge signal handler infrastructure

tipc: purge signal handler infrastructure

In the previous commits of this series, we removed all asynchronous
actions which were based on the tasklet handler - "tipc_k_signal()".

So the moment has now come when we can completely remove the tasklet
handler infrastructure. That is done with this commit.

Signed-off-by: Ying Xue <[email protected]>
Reviewed-by: Erik Hugne <[email protected]>
Reviewed-by: Jon Maloy <[email protected]>
Signed-off-by: David S. Miller <[email protected]>