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 37724ac2c3 for now.

components/backlight.c

@@ -1,32 +0,0 @@
-/* See LICENSE file for copyright and license details. */
-#include "../util.h"
-
-#if defined(__linux__)
-	#include <limits.h>
-
-	#define BRIGHTNESS_MAX "/sys/class/backlight/%s/max_brightness"
-	#define BRIGHTNESS_CUR "/sys/class/backlight/%s/brightness"
-
-	const char *
-	backlight_perc(const char *card)
-	{
-		char path[PATH_MAX];
-		int max, cur;
-
-		if (esnprintf(path, sizeof (path), BRIGHTNESS_MAX, card) < 0 ||
-			pscanf(path, "%d", &max) != 1) {
-			return NULL;
-		}
-
-		if (esnprintf(path, sizeof (path), BRIGHTNESS_CUR, card) < 0 ||
-			pscanf(path, "%d", &cur) != 1) {
-			return NULL;
-		}
-
-		if (max == 0) {
-			return NULL;
-		}
-
-		return bprintf("%d", cur * 100 / max);
-	}
-#endif