task-x11-illume: change default ETHEME from e-wm-theme-illume to e-wm-theme-default

* e-wm-theme-illume is gone with illume1 (see b37564b7

)
* found by accident when running distroless build, guess everybody is using own theme anyway

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>