Fix use after free when an event listener is destroyed
Fix use after free when an event listener is destroyed

Properly remove event listeners from the list when they are deregistered.
Fixes a crash that can happen when orca exits. Similar issue to
https://gitlab.gnome.org/GNOME/at-spi2-core/issues/22

GNOME/at-spi2-core,GNOME/at-spi2-core,GNOME/at-spi2-core