Revert "Use given connections id in connection_disappeared()."
This reverts src/{network,sched}/connection.c CVS revision 1.43,
which was made on 2003-07-03 and converted to Git commit
cae65f7941628109b51ffb2e2d05882fbbdc73ef in elinks-history.
It is pointless to check whether (c == d && c->id == d->id).
If c == d, then surely c->id == d->id, and I wouldn't be surprised
to see a compiler optimize that out.
Whereas, by taking the id as a parameter, connection_disappeared()
can check whether the pointer now points to a new struct connection
with a different id.