Add $ANDROID_PRODUCT_OUT/apex to installclean.

When removing dependencies from APEXes, the lib files were still there
even after installclean.

Bug: 139016109
Test: run installclean, see apex directories go away :D
Change-Id: I4dad8e3aa0042cdd5bbb76bd6fdd01b025b98495
diff --git a/ui/build/cleanbuild.go b/ui/build/cleanbuild.go
index 8e7f96a..bfe2c36 100644
--- a/ui/build/cleanbuild.go
+++ b/ui/build/cleanbuild.go
@@ -99,6 +99,7 @@
 		productOut("*.img"),
 		productOut("*.zip"),
 		productOut("android-info.txt"),
+		productOut("apex"),
 		productOut("kernel"),
 		productOut("data"),
 		productOut("skin"),