io/gpio: remove the deprecated doc

If no driver is provided, Open panics.

Change-Id: I10b93fa51e923b226db5d1f62bb7a00c09da2e7a
Reviewed-on: https://go-review.googlesource.com/24218
Reviewed-by: Johan Euphrosine <proppy@google.com>
Reviewed-by: Matt Aimonetti <mattaimonetti@gmail.com>
Reviewed-by: Jaana Burcu Dogan <jbd@google.com>
1 file changed