[mesh-forwarder] remove unused SetDiscoverParameters() method (#10420)

src/core/thread/mesh_forwarder.hpp

@@ -240,15 +240,6 @@ public:
      */
     void SetRxOnWhenIdle(bool aRxOnWhenIdle);
 
-    /**
-     * Sets the scan parameters for MLE Discovery Request messages.
-     *
-     * @param[in]  aScanChannels  A reference to channel mask indicating which channels to scan.
-     *                            If @p aScanChannels is empty, then all channels are used instead.
-     *
-     */
-    void SetDiscoverParameters(const Mac::ChannelMask &aScanChannels);
-
 #if OPENTHREAD_FTD
     /**
      * Frees any messages queued for an existing child.