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: I052dc77c4d7f4304cc163864dd000beccf708a2a

openstack/swift,openstack/swift,openstack/swift,tipabu/swift,openstack/swift,tipabu/swift,tipabu/swift,tipabu/swift