beaglebone: Drop the deprecated GPIO_SYSFS

In order to fix the following configcheck warning:
  [NOTE]: 'CONFIG_GPIO_SYSFS' last val (y) and .config val (n) do not match
  [INFO]: CONFIG_GPIO_SYSFS : n
  [INFO]: raw config text:

      config GPIO_SYSFS
      	bool "/sys/class/gpio/... (sysfs interface)" if EXPERT
      	select GPIO_CDEV
      	depends on SYSFS && GPIOLIB
      	help
      	  Say Y here to add the legacy sysfs interface for GPIOs.

      	  This ABI is deprecated. If you want to use GPIO from userspace,
      	  use the character device /dev/gpiochipN with the appropriate
      	  ioctl() operations instead.

      Config 'GPIO_SYSFS' has the following Direct dependencies (GPIO_SYSFS=y):
              SYSFS(=y) && GPIOLIB(=y)
      Parent dependencies are:
           GPIOLIB [y] EXPERT [n] SYSFS [y]
  [INFO]: config 'CONFIG_GPIO_SYSFS' was set, but it wasn't assignable, check (parent) dependencies

Signed-off-by: Kevin Hao <kexin.hao@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>

bsp/beaglebone/beaglebone.cfg

@@ -148,7 +148,6 @@ CONFIG_PINMUX=y
 CONFIG_PINCONF=y
 CONFIG_GENERIC_PINCONF=y
 CONFIG_PINCTRL_SINGLE=y
-CONFIG_GPIO_SYSFS=y
 
 #
 # I2C GPIO expanders: