gs101: clean up kernel variables

1) remove TARGET_BOARD_KERNEL_HEADERS
2) remove TARGET_PREBUILT_KERNEL

Bug: 198682676
Change-Id: I9ab161ee75dc33e135ad87e084b3373350ca0c93
diff --git a/BoardConfig-common.mk b/BoardConfig-common.mk
index a3dcda0..0d67432 100644
--- a/BoardConfig-common.mk
+++ b/BoardConfig-common.mk
@@ -323,8 +323,6 @@
 BOARD_BLUETOOTH_BDROID_BUILDCFG_INCLUDE_DIR := \
 	build/make/target/board/mainline_arm64/bluetooth
 
-TARGET_BOARD_KERNEL_HEADERS := $(TARGET_KERNEL_DIR)/kernel-headers
-
 #VNDK
 BOARD_PROPERTY_OVERRIDES_SPLIT_ENABLED := true
 BOARD_VNDK_VERSION := current
diff --git a/device.mk b/device.mk
index fee9ac0..b56eea4 100644
--- a/device.mk
+++ b/device.mk
@@ -48,11 +48,7 @@
 	vendor/google_nos/host/android \
 	vendor/google_nos/test/system-test-harness
 
-ifeq ($(TARGET_PREBUILT_KERNEL),)
 LOCAL_KERNEL := $(TARGET_KERNEL_DIR)/Image.lz4
-else
-LOCAL_KERNEL := $(TARGET_PREBUILT_KERNEL)
-endif
 
 # OEM Unlock reporting
 PRODUCT_DEFAULT_PROPERTY_OVERRIDES += \