ARM: omap1: Drop header on AMS Delta

The AMS Delta board uses GPIO descriptors exclusively and
does not have any dependencies on the legacy <linux/gpio.h>
header, so just drop it.

Acked-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Fixes: 92bf78b3 ("gpio: omap: use dynamic allocation of base")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>