MoKeeSetupWizard: fix crash when quickly skipping through pages

It is possible that the writeDisableNavKeyOption delayed runnable
actions run after the fragment is detached. Remove callbacks when the
fragment is detached to avoid this.

Change-Id: I7500f0839dad06a531c8db595de2d3a69ea3468c
Signed-off-by: Roman Birg <roman@cyngn.com>