doc: Comment out language option
doc: Comment out language option

... because explicit language=None causes the below warning since
Sphinx 5.0.0.

Invalid configuration value found: 'language = None'. Update your
configuration to a valid language code. Falling back to 'en' (English).

Change-Id: I842fd6c1eb5c0e14d85f8eec6078d735fbd506b8

openstack/python-swiftclient,sohonetlabs/python-swiftclient,openstack/python-swiftclient,sohonetlabs/python-swiftclient