Revert "Revert "Remove "fire_event" from AsyncClientMixin, since this was only added to remove infinite recusion in the reactor-- which is now not calling this API""

This reverts commit ba7f08d047afffc2b87950910cac0cdd48b76302.
Revert "Revert "Remove some un-used variables""

This reverts commit 82b5567c9248f345e2b388e3d238d51b7a0d9640.
Revert "Revert "Pylint cleanup for threadpool""

This reverts commit 32d01ee6c6bd4a7070be158c7188ede14cb34b60.