Mark ANDROID_BUILD_TOP as obsolete

All users have been removed.

Test: check the build_test logs from aosp/master -> goog/master
Change-Id: I99e5630d7c13882c7667b0499c4f55633fa4535a
diff --git a/core/config.mk b/core/config.mk
index 4a0c540..2f7a216 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -67,7 +67,7 @@
 $(KATI_obsolete_var ANDROID_PRODUCT_OUT,Use PRODUCT_OUT instead. See $(CHANGES_URL)#ANDROID_PRODUCT_OUT)
 $(KATI_obsolete_var ANDROID_HOST_OUT_TESTCASES,Use HOST_OUT_TESTCASES instead. See $(CHANGES_URL)#ANDROID_HOST_OUT_TESTCASES)
 $(KATI_obsolete_var ANDROID_TARGET_OUT_TESTCASES,Use TARGET_OUT_TESTCASES instead. See $(CHANGES_URL)#ANDROID_TARGET_OUT_TESTCASES)
-$(KATI_deprecated_var ANDROID_BUILD_TOP,Use '.' instead. See $(CHANGES_URL)#ANDROID_BUILD_TOP)
+$(KATI_obsolete_var ANDROID_BUILD_TOP,Use '.' instead. See $(CHANGES_URL)#ANDROID_BUILD_TOP)
 $(KATI_obsolete_var \
   ANDROID_TOOLCHAIN \
   ANDROID_TOOLCHAIN_2ND_ARCH \