ElectricalSeries.channel_conversion not schema compliant

[oruebel]

ElectricalSeries.channel_conversion is:

• missing the attribute axis, which should be int32 with a fixed value of 1
• has extra attributes for object_id, description and namespace . Only objects with a specified neurodata_type should get these extra attributes.

I believe the following code should be removed:

aqnwb/src/nwb/ecephys/ElectricalSeries.cpp

Lines 63 to 66 in 33e3481

	m_io->createCommonNWBAttributes(getPath() + "/channel_conversion",
	"hdmf-common",
	"",
	"Bit volts values for all channels");

and the new int attribute axis should be added instead. This error is currently missing in the validation with nwbinspector due to #108

https://nwb-schema.readthedocs.io/en/latest/format.html#sec-electricalseries