Add `$ANDROID_HOST_OUT/apex` to the file set removed by target `installclean`.

Before this change, host APEX (`.zipapex`) packages would still be
there after `m installclean`.

Test: Run `m installclean` and check that host APEX packages are removed.
Change-Id: I446286ce700f12666be5aa90fbe3bbc648abd280

ui/build/cleanbuild.go

@@ -87,6 +87,7 @@ func installClean(ctx Context, config Config, what int) {
 	// otherwise we'd have to rebuild any generated files created with
 	// those tools.
 	removeGlobs(ctx,
+		hostOut("apex"),
 		hostOut("obj/NOTICE_FILES"),
 		hostOut("obj/PACKAGING"),
 		hostOut("coverage"),