fbdev/atafb: Remove unused extern variables

Remove 6 unused extern variables to reduce confusion. It is worth
mentioning that lib/fonts/font_8x8.c and lib/fonts/font_8x16.c also
declare `fontdata_8x8` and `fontdata_8x16` respectively, and this file
has nothing to do with them.
Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/cb5bb49a33ff54fef41e719ee9d301a6a73c5f9c.1603788512.git.yepeilin.cs@gmail.com
Link: https://patchwork.freedesktop.org/patch/msgid/20201028105647.1210161-1-yepeilin.cs@gmail.com

drivers/video/fbdev/atafb.c

@@ -240,14 +240,6 @@ static int *MV300_reg = MV300_reg_8bit;
 
 static int inverse;
 
-extern int fontheight_8x8;
-extern int fontwidth_8x8;
-extern unsigned char fontdata_8x8[];
-
-extern int fontheight_8x16;
-extern int fontwidth_8x16;
-extern unsigned char fontdata_8x16[];
-
 /*
  * struct fb_ops {
  *	* open/release and usage marking