Fix boards which were overriding backlight without setting custom (#7970)

keyboards/clueboard/66_hotswap/gen1/led.c

@@ -16,6 +16,5 @@
 */
 
 #include "hal.h"
-#include "backlight.h"
 #include "led.h"
 #include "printf.h"

keyboards/clueboard/66_hotswap/gen1/matrix.c

@@ -5,7 +5,6 @@
 #include "timer.h"
 #include "wait.h"
 #include "printf.h"
-#include "backlight.h"
 #include "matrix.h"
 #include "action.h"
 #include "keycode.h"

keyboards/clueboard/66_hotswap/gen1/rules.mk

@@ -7,7 +7,6 @@ LED_MATRIX_ENABLE = IS31FL3731
 # Build Options
 #   comment out to disable the options.
 #
-BACKLIGHT_ENABLE = yes
 BOOTMAGIC_ENABLE = yes	# Virtual DIP switch configuration
 ## (Note that for BOOTMAGIC on Teensy LC you have to use a custom .ld script.)
 MOUSEKEY_ENABLE = yes	# Mouse keys