gta4xl-common: Remove no-op TARGET_KERNEL_ARCH flag

TARGET_KERNEL_ARCH is a no-op unless it is different from TARGET_ARCH.

Change-Id: If36d5adc3296b76d5efb21da0e196f0b005ae784
diff --git a/BoardConfigCommon.mk b/BoardConfigCommon.mk
index eb05bdb..c42948e 100644
--- a/BoardConfigCommon.mk
+++ b/BoardConfigCommon.mk
@@ -111,7 +111,6 @@
 
 ## Kernel
 BOARD_KERNEL_IMAGE_NAME := Image
-TARGET_KERNEL_ARCH := arm64
 TARGET_KERNEL_SOURCE := kernel/samsung/gta4xl
 
 ## Keymaster