fix "declared and not used" in tests;
also template/template.go, missed last time.

R=r
DELTA=116  (61 added, 10 deleted, 45 changed)
OCL=34620
CL=34622
diff --git a/test/interface/fail.go b/test/interface/fail.go
index 0e0c4d3..07bd865 100644
--- a/test/interface/fail.go
+++ b/test/interface/fail.go
@@ -18,6 +18,7 @@
 	var e interface {};
 	e = s;
 	i = e.(I);
+	_ = i;
 }
 
 // hide S down here to avoid static warning