Remove -includePreview flag until support is available in doclava.

Change-Id: I3b644bd50d42ea260bed09c9c5bdab6d3d6a8b75
diff --git a/Android.mk b/Android.mk
index e9eab26..b4d21e4 100644
--- a/Android.mk
+++ b/Android.mk
@@ -1043,7 +1043,6 @@
 		-hdf android.whichdoc online \
 		$(sample_groups) \
 		-useUpdatedTemplates \
-		-includePreview \
 		-hdf android.hasSamples true \
 		-samplesdir $(samples_dir)