CLEANUP: external-check: don't block/unblock SIGCHLD when manipulating the list

CLEANUP: external-check: don't block/unblock SIGCHLD when manipulating the list

There's no point in blocking/unblocking sigchld when removing entries
from the list since the code is called asynchronously.

Similarly the blocking/unblocking could be removed from the connect_proc_chk()
function but it happens that at high signal rates, fork() takes twice as much
time to execute as it is regularly interrupted by a signal, so in the end this
signal blocking is beneficial there for performance reasons.