refactor(diag): delete unnecessary declarations

Author: strager

src/quick-lint-js/diag/diag-reporter.h

@@ -8,14 +8,6 @@ class Diag_List;
 
 class Diag_Reporter {
  public:
-  Diag_Reporter() = default;
-
-  Diag_Reporter(const Diag_Reporter &) = default;
-  Diag_Reporter &operator=(const Diag_Reporter &) = default;
-
-  Diag_Reporter(Diag_Reporter &&) = default;
-  Diag_Reporter &operator=(Diag_Reporter &&) = default;
-
   virtual ~Diag_Reporter() = default;
 
   virtual void report(const Diag_List &) = 0;