Clean vts-core in host/out to ensure old package to be removed.

Bug: None
Test: m installclean
Change-Id: I5aa451d87dc377e62dcf1b88baa58539fa661feb
diff --git a/ui/build/cleanbuild.go b/ui/build/cleanbuild.go
index 1dbeb26..0b44b4d 100644
--- a/ui/build/cleanbuild.go
+++ b/ui/build/cleanbuild.go
@@ -97,6 +97,7 @@
 		hostOut("sdk_addon"),
 		hostOut("testcases"),
 		hostOut("vts"),
+		hostOut("vts-core"),
 		productOut("*.img"),
 		productOut("*.zip"),
 		productOut("android-info.txt"),