ath79: switch to Kernel 5.10

Kernel 5.10 is used by many people since quite a while. With other
targets already moved to 5.10, let ath79 follow suit.

Tested-by: Stefan Lippers-Hollmann <s.l-h@gmx.de> [ath79/tl-wdr3600; ath79/tl-wdr4300]
Tested-by: Aleksander Jan Bajkowski <olek2@wp.pl> [ath79/tl-wdr4300]
Signed-off-by: NPaul Spooren <mail@aparcar.org>
Signed-off-by: NDavid Bauer <mail@david-bauer.net>

target/linux/ath79/Makefile

@@ -8,8 +8,7 @@ SUBTARGETS:=generic mikrotik nand tiny
 
 FEATURES:=ramdisk squashfs usbgadget
 
-KERNEL_PATCHVER:=5.4
-KERNEL_TESTING_PATCHVER:=5.10
+KERNEL_PATCHVER:=5.10
 
 include $(INCLUDE_DIR)/target.mk