[mac] fix warning in mac_types.hpp (#4889)

src/core/mac/mac_types.hpp

@@ -73,8 +73,6 @@ typedef otPanId PanId;
  */
 typedef otShortAddress ShortAddress;
 
-#if !OPENTHREAD_RADIO
-
 /**
  * This function generates a random IEEE 802.15.4 PAN ID.
  *
@@ -83,8 +81,6 @@ typedef otShortAddress ShortAddress;
  */
 PanId GenerateRandomPanId(void);
 
-#endif
-
 /**
  * This structure represents an IEEE 802.15.4 Extended Address.
  *