Remove droiddoc.mk from Make!

Test: m -j
Bug: b/70351683, b/78245848
Change-Id: I3348461d742c45d5dae105d26a5c3e8680a08029
diff --git a/core/config.mk b/core/config.mk
index f3be496..db2155c 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -84,6 +84,7 @@
   ,See $(CHANGES_URL)#other_envsetup_variables)
 $(KATI_obsolete_var PRODUCT_COMPATIBILITY_MATRIX_LEVEL_OVERRIDE,Set FCM Version in device manifest instead. See $(CHANGES_URL)#PRODUCT_COMPATIBILITY_MATRIX_LEVEL_OVERRIDE)
 $(KATI_obsolete_var USE_CLANG_PLATFORM_BUILD,Clang is the only supported Android compiler. See $(CHANGES_URL)#USE_CLANG_PLATFORM_BUILD)
+$(KATI_obsolete_var BUILD_DROIDDOC,Droiddoc is only supported in Soong. See details on build/soong/java/droiddoc.go)
 
 # This is marked as obsolete in envsetup.mk after reading the BoardConfig.mk
 $(KATI_deprecate_export It is a global setting. See $(CHANGES_URL)#export_keyword)
@@ -146,7 +147,6 @@
 BUILD_JAVA_LIBRARY:= $(BUILD_SYSTEM)/java_library.mk
 BUILD_STATIC_JAVA_LIBRARY:= $(BUILD_SYSTEM)/static_java_library.mk
 BUILD_HOST_JAVA_LIBRARY:= $(BUILD_SYSTEM)/host_java_library.mk
-BUILD_DROIDDOC:= $(BUILD_SYSTEM)/droiddoc.mk
 BUILD_APIDIFF:= $(BUILD_SYSTEM)/apidiff.mk
 BUILD_COPY_HEADERS := $(BUILD_SYSTEM)/copy_headers.mk
 BUILD_NATIVE_TEST := $(BUILD_SYSTEM)/native_test.mk