LED: drop leds-ams-delta driver

This driver is no longer needed after the Amstrad Delta on-board LED
devices have been converted to leds-gpio compatible.

Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>