Do not use variadic sink fn in tests

Author: owen-mc

go/ql/test/experimental/frameworks/CleverGo/UntrustedSources.go

@@ -7,6 +7,6 @@ func source() interface{} {
 	return nil
 }
 
-func sink(v ...interface{}) {}
+func sink(v interface{}) {}
 
 func link(from interface{}, into interface{}) {}

go/ql/test/experimental/frameworks/CleverGo/stubs.go

@@ -7,6 +7,6 @@ func source() interface{} {
 	return nil
 }
 
-func sink(v ...interface{}) {}
+func sink(v interface{}) {}
 
 func link(from interface{}, into interface{}) {}