fix: Module type always empty string

The change in #2270 accidentally broke how we access module types.
module<Impl>::TYPE always points to the module superclass and it thus
accesses its empty TYPE field.

This mainly broke legacy action handling.

Ref #2270

include/modules/meta/base.hpp

@@ -148,8 +148,6 @@ namespace modules {
 
     bool input(const string& action, const string& data);
 
-    static constexpr auto TYPE = "";
-
    protected:
     void broadcast();
     void idle();

include/modules/meta/base.inl

@@ -48,7 +48,7 @@ namespace modules {
 
   template <typename Impl>
   string module<Impl>::type() const {
-    return string(module<Impl>::TYPE);
+    return string(Impl::TYPE);
   }
 
   template <typename Impl>