iio: ABI: remove duplicate in_resistance_calibbias

In commit 0f718e10da81 ("iio: ABI: add missing calibbias attributes"),
the in_resistance_calibbias attribute was added to the main IIO ABI
documentation. This attribute is was already documented in
sysfs-bus-iio-chemical-sgp40. This resulted in a duplicate entry that is
causing documentation build warnings.

This removes the attribute from the sgp40 documentation in favor of the
main IIO ABI documentation since this attribute fits the established
pattern of standard IIO attributes.

Reported-by: Stephen Rothwell <[e-mail]>
Closes: https://lore.kernel.org/linux-next/[e-mail]/
Signed-off-by: David Lechner <[e-mail]>
Link: https://patch.msgid.link/20240[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

Documentation/ABI/testing/sysfs-bus-iio-chemical-sgp40

···
 		Set the relative humidity. This value is sent to the sensor for
 		humidity compensation.
 		Default value: 50000 (50 % relative humidity)
-
-What:		/sys/bus/iio/devices/iio:deviceX/in_resistance_calibbias
-Date:		August 2021
-KernelVersion:	5.15
-Contact:	Andreas Klinger <[e-mail]>
-Description:
-		Set the bias value for the resistance which is used for
-		calculation of in_concentration_input as follows:
-
-		x = (in_resistance_raw - in_resistance_calibbias) * 0.65
-
-		in_concentration_input = 500 / (1 + e^x)
-
-		Default value: 30000