Fix stuck modifiers on client exit

Fix stuck modifiers on client exit

Summary:
We still need to remove the active keys when focus_out happens, even
if the pixmap is already gone.  If we don't and a modifier was held
down during exit then the xkb state will have that modifier stuck
forever.

Reviewers: zmike, devilhorns

Subscribers: cedric

Differential Revision: https://phab.enlightenment.org/D2110