Event connectionFailed is trigerred only when a connection do not succeed,
meaning that the connection was never opened and no packets could have
been sent or received through it. Here the unregistration from the
dispatcher was useless in case of a connection failed.
Remove the related XXX.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@1736 71dcc9de-d417-0410-9af5-da40c76e7ee4