Removed dead code

src/sequence_diagram/model/participant.h

@@ -193,20 +193,6 @@ private:
     std::string full_name_;
 };
 
-/**
- * @brief Participant representing a C++ lambda.
- */
-struct lambda : public class_ {
-    using class_::class_;
-
-    /**
-     * Get the type name of the diagram element.
-     *
-     * @return Type name of the diagram element.
-     */
-    std::string type_name() const override { return "lambda"; }
-};
-
 /**
  * @brief Participant mode representing a free function.
  */