Remove references to non-existant directories

Fixes warnings during makefile parsing:
FindEmulator: find: `prebuilts/tools/android-arm64': No such file or directory

Test: builds
Change-Id: I1e261e0d6e29bdefc7e325c6efb8fd2d85f6810c
diff --git a/Android.mk b/Android.mk
index 6238bd8..ccc86bf 100644
--- a/Android.mk
+++ b/Android.mk
@@ -17,5 +17,4 @@
 
 include $(call first-makefiles-under, \
 		$(LOCAL_PATH)/common \
-		$(LOCAL_PATH)/$(TARGET_PREBUILT_TAG) \
 		$(LOCAL_PATH)/$(HOST_PREBUILT_TAG)) \