Remove GlobalWindowManager close listener.

The entire client may break, this does seem to do quite a lot.

Change-Id: Iba95186773bc8f79907a051d0eaad78cb1849e37
Reviewed-on: http://gerrit.dmdirc.com/3783
Reviewed-by: Chris Smith <chris@dmdirc.com>
Automatic-Compile: DMDirc Build Manager