delete unused IOCTL MAGIOCGSAMPLERATE

src/drivers/drv_mag.h

src/drivers/imu/adis16448/adis16448.cpp

src/drivers/imu/fxos8701cq/fxos8701cq.cpp

src/drivers/imu/lsm303d/lsm303d.cpp

src/drivers/imu/mpu9250/mag.cpp

src/drivers/magnetometer/bmm150/bmm150.cpp

src/drivers/magnetometer/hmc5883/hmc5883.cpp

src/drivers/magnetometer/ist8310/ist8310.cpp

src/drivers/magnetometer/lis3mdl/lis3mdl.cpp

src/drivers/magnetometer/lsm303agr/LSM303AGR.cpp

src/drivers/magnetometer/rm3100/rm3100.cpp

src/modules/simulator/accelsim/accelsim.cpp

src/modules/uavcan/sensors/mag.cpp

src/systemcmds/config/config.c