delete unused IOCTL MAGIOCGSAMPLERATE

src/drivers/magnetometer/lis3mdl/lis3mdl.cpp

@@ -584,10 +584,6 @@ LIS3MDL::ioctl(struct file *file_pointer, int cmd, unsigned long arg)
 	case SENSORIOCRESET:
 		return reset();
 
-	case MAGIOCGSAMPLERATE:
-		/* same as pollrate because device is in single measurement mode*/
-		return 1000000 / TICK2USEC(_measure_ticks);
-
 	case MAGIOCSRANGE:
 		return set_range(arg);