Fix compiler warning unused variable kill_message.

(cherry picked from commit 54e2b6a829a221cc3abbff3a39ca7d3cafed3a09)
Pick only unused kill_message.

Firmware/Marlin_main.cpp

@@ -4977,7 +4977,6 @@ if(eSoundMode!=e_SOUND_MODE_SILENT)
 		}
 		#endif // SUPPORT_VERBOSITY
 		int l_feedmultiply = setup_for_endstop_move(false); //save feedrate and feedmultiply, sets feedmultiply to 100
-		const char *kill_message = NULL;
 		while (mesh_point != nMeasPoints * nMeasPoints) {
 			// Get coords of a measuring point.
 			uint8_t ix = mesh_point % nMeasPoints; // from 0 to MESH_NUM_X_POINTS - 1