tpl: Fix the remaining template funcs namespace issues

See #3042

tpl/os/os.go

@@ -35,9 +35,6 @@ type Namespace struct {
 	deps *deps.Deps
 }
 
-// Namespace returns a pointer to the current namespace instance.
-func (ns *Namespace) Namespace() *Namespace { return ns }
-
 // Getenv retrieves the value of the environment variable named by the key.
 // It returns the value, which will be empty if the variable is not present.
 func (ns *Namespace) Getenv(key interface{}) (string, error) {