auxdisplay: ht16k33: remove superfluous header files

ht16k33.c doesn't use any macro or function declared in
linux/slab.h. Thus, these files can be removed from ht16k33.c
safely without affecting the compilation.

Signed-off-by: Mianhan Liu <liumh1@shanghaitech.edu.cn>
Acked-by: Robin van der Gracht <robin@protonic.nl>
[reworded]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: oscarliu2019

drivers/auxdisplay/ht16k33.c

@@ -14,7 +14,6 @@
 #include <linux/i2c.h>
 #include <linux/property.h>
 #include <linux/fb.h>
-#include <linux/slab.h>
 #include <linux/backlight.h>
 #include <linux/input.h>
 #include <linux/input/matrix_keypad.h>