ar71xx: remove obsolete '< KERNEL_VERSION(4, 4, 0)' check

Because the oldest supported kernel version on the ar71xx target is 4.4,
the condition that the kernel version is smaller than 4.4.0 is always
false. Remove the obsolete check from mach-rb4xx.c to clean up the code
a bit.

Signed-off-by: Gabor Juhos <juhosg@freemail.hu>

target/linux/ar71xx/files/arch/mips/ath79/mach-rb4xx.c

@@ -11,12 +11,7 @@
 
 #include <linux/platform_device.h>
 #include <linux/irq.h>
-#include <linux/version.h>
-#if LINUX_VERSION_CODE < KERNEL_VERSION(4,4,0)
-#include <linux/mdio-gpio.h>
-#else
 #include <linux/platform_data/mdio-gpio.h> 
-#endif
 #include <linux/mmc/host.h>
 #include <linux/spi/spi.h>
 #include <linux/spi/flash.h>