leds: Remove SEAD-3 driver

SEAD3 is using the generic syscon & regmap based register-bit-led
driver as of commit c764583f ("MIPS: SEAD3: Use register-bit-led
driver via DT for LEDs") merged in the v4.9 cycle. As such the custom
SEAD-3 LED driver is now unused, so remove it.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: linux-leds@vger.kernel.org
Cc: linux-mips@linux-mips.org
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>