auxdisplay: cfag12864bfb: remove superfluous header files

cfag12864bfb.c doesn't use any macro or function declared in
linux/delay.h, linux/string.h and linux/uaccess.h. Thus,
these files can be removed from cfag12864bfb.c safely without
affecting the compilation.

Signed-off-by: Mianhan Liu <liumh1@shanghaitech.edu.cn>
[reworded]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>