atyfb: remove dead code

Remove dead code.  This will slightly change the behaviour of the driver
on systems that support backlight control.  Previously they would just
turn the backlight off using the backlight control but now the generic LCD
code will also turn off the LCD using the POWER_MANAGEMENT register.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: Ville Syrjala <syrjala@sci.fi>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>