[mac] clear mode2 key only on mac destruction

src/core/mac/mac.hpp

@@ -134,6 +134,11 @@ public:
      */
     explicit Mac(Instance &aInstance);
 
+    /**
+     * Clears the Mode2Key on destruction.
+     */
+    ~Mac(void) { ClearMode2Key(); }
+
     /**
      * Starts an IEEE 802.15.4 Active Scan.
      *

src/core/thread/key_manager.cpp

@@ -691,7 +691,6 @@ void KeyManager::DestroyTemporaryKeys(void)
     mMleKey.Clear();
     mKek.Clear();
     Get<Mac::SubMac>().ClearMacKeys();
-    Get<Mac::Mac>().ClearMode2Key();
 }
 
 void KeyManager::DestroyPersistentKeys(void) { Get<Crypto::Storage::KeyRefManager>().DestroyPersistentKeys(); }