core: Add missing override specifiers where applicable

Applies the override specifier where applicable. In the case of
destructors that are  defaulted in their definition, they can
simply be removed.

This also removes the unnecessary inclusions being done in audin_u and
audrec_u, given their close proximity.

src/core/loader/xci.h

@@ -22,7 +22,7 @@ class AppLoader_NCA;
 class AppLoader_XCI final : public AppLoader {
 public:
     explicit AppLoader_XCI(FileSys::VirtualFile file);
-    ~AppLoader_XCI();
+    ~AppLoader_XCI() override;
 
     /**
      * Returns the type of the file