No need to check for the existence of the variable to destroy it.

Destroying directly saves one Lookup.

src/audio_output/dec.c

@@ -231,15 +231,9 @@ int aout_DecDelete( aout_instance_t * p_aout, aout_input_t * p_input )
     {
         aout_OutputDelete( p_aout );
         aout_MixerDelete( p_aout );
-        if ( var_Type( p_aout, "audio-device" ) != 0 )
-        {
         var_Destroy( p_aout, "audio-device" );
-        }
-        if ( var_Type( p_aout, "audio-channels" ) != 0 )
-        {
         var_Destroy( p_aout, "audio-channels" );
     }
-    }
 
     aout_unlock_mixer( p_aout );
 

src/audio_output/intf.c

@@ -440,14 +440,8 @@ int aout_FindAndRestart( vlc_object_t * p_this, const char *psz_name,
     (void)psz_name; (void)oldval; (void)newval; (void)p_data;
     if ( p_aout == NULL ) return VLC_SUCCESS;
 
-    if ( var_Type( p_aout, "audio-device" ) != 0 )
-    {
     var_Destroy( p_aout, "audio-device" );
-    }
-    if ( var_Type( p_aout, "audio-channels" ) != 0 )
-    {
     var_Destroy( p_aout, "audio-channels" );
-    }
 
     aout_Restart( p_aout );
     vlc_object_release( p_aout );
@@ -469,11 +463,8 @@ int aout_ChannelsRestart( vlc_object_t * p_this, const char * psz_variable,
     {
         /* This is supposed to be a significant change and supposes
          * rebuilding the channel choices. */
-        if ( var_Type( p_aout, "audio-channels" ) >= 0 )
-        {
         var_Destroy( p_aout, "audio-channels" );
     }
-    }
     aout_Restart( p_aout );
     return 0;
 }