Remove BUILD_DROIDDOC

BUILD_DROIDDOC is obsolete from Q and is no longer
supported in make system.

Droiddoc is only supported in Soong.

Change-Id: Ie61c571a2e0633c210c0db553609aa7d2862764b
diff --git a/Android.mk b/Android.mk
index 455895d..88017ee 100644
--- a/Android.mk
+++ b/Android.mk
@@ -44,6 +44,4 @@
 LOCAL_MODULE_CLASS := JAVA_LIBRARIES
 LOCAL_DROIDDOC_USE_STANDARD_DOCLET := true
 
-include $(BUILD_DROIDDOC)
-
 endif # JAVA_SUPPORT