Remove test output in ckati_clean

Fixes https://github.com/google/kati/issues/65

Change-Id: If1efb37f5d80ffe3f0972c6aa3090c39a0d96891
diff --git a/Makefile.ckati b/Makefile.ckati
index 377e36d..df4c6a5 100644
--- a/Makefile.ckati
+++ b/Makefile.ckati
@@ -126,6 +126,7 @@
 	rm -rf $(KATI_INTERMEDIATES_PATH)/*.d
 	rm -rf $(KATI_INTERMEDIATES_PATH)/version.cc
 	rm -rf $(KATI_CXX_TEST_EXES)
+	rm -rf out
 
 .PHONY: ckati_clean