Remove unused global variables in Makefiles

Change-Id: I31610b49e26e5383fea21732fe9cb228f3eebd73
diff --git a/preamble.mk b/preamble.mk
index 1065701..4f3de09 100644
--- a/preamble.mk
+++ b/preamble.mk
@@ -45,14 +45,6 @@
 	QEMU_ARCH := aarch64
 endif
 
-# Globally useful directories
-TOOLCHAIN := $(ROOTDIR)/toolchains/aarch64-linux-android/bin/aarch64-linux-android-
-
-# Kernel directories and options
-KERNEL_SRC_DIR := $(ROOTDIR)/linux-imx
-KERNEL_OUT_DIR := $(PRODUCT_OUT)/obj/KERNEL_OBJ
-KERNEL_OPTIONS := ARCH=arm64 CROSS_COMPILE=$(TOOLCHAIN) LOCALVERSION=-aiy
-
 FETCH_PBUILDER_DIRECTORY ?= /google/data/ro/teams/spacepark/enterprise/kokoro/prod/spacepark/enterprise/pbuilder
 FETCH_PBUILDER_BASE ?= $(IS_GLINUX)