apm821xx: move to 4.19 kernels

The 4.19 code has been available for some time now.
Since the f2fs / loop issue has been under control
I think it's time the target gets to move to it.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

target/linux/apm821xx/Makefile

@@ -13,8 +13,7 @@ MAINTAINER:=Chris Blake <chrisrblake93@gmail.com>, \
 	    Christian Lamparter <chunkeey@gmail.com>
 SUBTARGETS:=nand sata
 
-KERNEL_PATCHVER:=4.14
-KERNEL_TESTING_PATCHVER := 4.19
+KERNEL_PATCHVER:=4.19
 
 define Target/Description
 	Build images for AppliedMicro APM821xx based boards.