Adjust fullscreen toolbar's action names

Makes the toolbar work again after e2723eaf.

https://bugzilla.gnome.org/show_bug.cgi?id=741050
EogWindow: remove zoom-fit action

https://bugzilla.gnome.org/show_bug.cgi?id=741050
EogWindow: Use gtk_widget_set_visible
EogWindow: Drop unneeded handler blocks

As the action state is now changed without triggering the handlers
they don't need to be blocked anymore.

https://bugzilla.gnome.org/show_bug.cgi?id=741050