removed ENTT_API from ENTT_OPAQUE_ID

TODO

@@ -30,10 +30,7 @@
     * meta: use type_id, remove import, everything should work transparently
     * type_id_enabled and fallback on old-fashioned families otherwise
     * add discard pool functionality (+ test)
-  - clean up target_compile_definitions test/CMakeLists.txt (_EXPORT/_IMPORT)
   - use type_id also for groups, get rid of extent and subfunctions, is it possible?
-  - families should be defined as out-of-class to guarantee the same identifiers for the same types
   - update doc: dispatcher, emitter, registry, meta, across boundaries
   - update/improve/review tests
   - review and suppress warnings, if any
-  - remove ENTT_API from OPAQUE_TYPE

src/entt/core/type_traits.hpp

@@ -5,7 +5,6 @@
 #include <cstddef>
 #include <type_traits>
 #include "../config/config.h"
-#include "../core/attribute.h"
 #include "../core/hashed_string.hpp"
 
 
@@ -177,7 +176,7 @@ constexpr auto is_equality_comparable_v = is_equality_comparable<Type>::value;
  * @param type The underlying type for the enum class.
  */
 #define ENTT_OPAQUE_TYPE(clazz, type)\
-    enum class ENTT_API clazz: type {};\
+    enum class clazz: type {};\
     constexpr auto to_integral(const clazz id) ENTT_NOEXCEPT {\
         return std::underlying_type_t<clazz>(id);\
     }\