remove useless (at best, harmful) feature test checks in aio.h

include/aio.h

@@ -5,9 +5,6 @@
 extern "C" {
 #endif
 
-#if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
- || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE)
-
 #include <signal.h>
 #include <time.h>
 
@@ -51,8 +48,6 @@ int aio_fsync(int, struct aiocb *);
 
 int lio_listio(int, struct aiocb *const [], int, struct sigevent *);
 
-#endif
-
 #ifdef __cplusplus
 }
 #endif