evdev: remove tag_device from evdev_dispatch_interface

evdev: remove tag_device from evdev_dispatch_interface

Tagging a device should occur only once during configure. We do not
have devices that can be changed after they are configured, so there is no
point in having the tagging part in a deferred struct.
Plus, the note saying that we tag with only one of EVDEV_TAG was wrong.

Now that we are chosing when we call each evdev_tag_*, we can also get
rid of the device->seat_caps tests.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>