Revert "Add basic backlight percentage support"

On OpenBSD the backlight percentage cannot be retrieved in a simple way.
The only two solutions we are aware of for now are:

 - reading from /dev/ttyC0: which isn't possible without changing
 permissions or running slstatus as root
 - linking against xcb-xrandr: which is bloat and does not work in every
 case appearently

This reverts commit 37724ac for now.

Author: drkhsh

Makefile

@@ -6,7 +6,6 @@ include config.mk
 
 REQ = util
 COM =\
-	components/backlight\
 	components/battery\
 	components/cpu\
 	components/datetime\

README

@@ -6,7 +6,6 @@ slstatus is a suckless status monitor for window managers that use WM_NAME
 
 Features
 --------
-- Backlight percentage
 - Battery percentage/state/time left
 - CPU usage
 - CPU frequency

components/backlight.c

@@ -12,8 +12,6 @@ static const char unknown_str[] = "n/a";
 /*
  * function             description                     argument (example)
  *
- * backlight_perc       backlight percentage            device name
- *                                                      (intel_backlight)
  * battery_perc         battery percentage              battery name (BAT0)
  *                                                      NULL on OpenBSD
  * battery_state        battery charging state          battery name (BAT0)

config.def.h

@@ -1,8 +1,5 @@
 /* See LICENSE file for copyright and license details. */
 
-/* backlight */
-const char *backlight_perc(const char *);
-
 /* battery */
 const char *battery_perc(const char *);
 const char *battery_state(const char *);

slstatus.h

@@ -1,6 +1,4 @@
 /* See LICENSE file for copyright and license details. */
-#include <stddef.h>
-
 extern char buf[1024];
 
 #define LEN(x) (sizeof (x) / sizeof *(x))