Aphlict - remove listeners when clients close the connection

Summary: Ref T7110. Listeners are now removed when clients close the connection to avoid stacking a never ending number of unused listeners.

Test Plan: Using wscat to connect to the Aphlict server; when closing the connection a 'Diconnected.' will appear in the logs and the number of active listeners is decreased by one.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T7110

Differential Revision: https://secure.phabricator.com/D11634