Close Channel on irc_amqp_listener termination.

Close Channel on irc_amqp_listener termination.

This fixes a bug wherein application:stop(irc) would leave a dangling Channel
that was consuming messages on a queue -- long after the process to which it
would deliver is dead.  That would cause the AMQP channel to exit with reason
unexpected_delivery_and_no_default_consumer, killing all of the rest of the
AMQP client and, by the transitive property of death, the irc application as
well.

The irc_amqp_listener must trap exits in order to receive a termination notice
from its supervisor.  I'm not actually sure if this has any implications for it
monitoring its AMQP Channel or not.