ist8310: remove calibration code

- it does nothing useful
- increases boot time by 2 seconds on pixhawk 4 due to a poll timeout:
IST8310 on I2C bus 3 at 0x0e (bus: 100 KHz, max: 400 KHz)
WARN  [ist8310] ERROR: TIMEOUT 2

boards/nxp/fmuk66-v3/init/rc.board_sensors

@@ -8,7 +8,7 @@ adc start
 # Possible external compasses
 hmc5883 -C -X start
 lis3mdl -X start
-ist8310 -C -b 1 start
+ist8310 -b 1 start
 qmc5883 -X start
 
 # Internal Mag I2C bus roll 180, yaw 90

boards/nxp/fmurt1062-v1/init/rc.board_sensors

@@ -30,8 +30,8 @@ bmi055 -A -R 10 start
 bmi055 -G -R 10 start
 
 # Possible external compasses
-ist8310 -C -b 1 start
-ist8310 -C -b 2 start
+ist8310 -b 1 start
+ist8310 -b 2 start
 hmc5883 -C -T -X start
 qmc5883 -X start
 lis3mdl -X start
@@ -44,7 +44,7 @@ then
 fi
 
 # Possible internal compass
-ist8310 -C -b 5 start
+ist8310 -b 5 start
 
 # Baro on internal SPI
 ms5611 -s start