Remove unnecessary dependency of the sdk target.

ALL_GENERATED_SOURCES forces to build heavy things already covered by
build cache.

Change-Id: I362bc450b9e303120d12ee8d53d75e86ef71e58f
diff --git a/core/Makefile b/core/Makefile
index fadec15..04fab18 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -1601,7 +1601,6 @@
 ATREE_FILES := \
 	$(ALL_PREBUILT) \
 	$(ALL_COPIED_HEADERS) \
-	$(ALL_GENERATED_SOURCES) \
 	$(ALL_DEFAULT_INSTALLED_MODULES) \
 	$(INSTALLED_RAMDISK_TARGET) \
 	$(ALL_DOCS) \