trivial: Fix comments in sphinxext module
trivial: Fix comments in sphinxext module

Comments shouldn't lie and these ones weren't updated to reflect recent
changes in the feature. Correct this here.

Change-Id: I56e9a49f15948a0f056c5bb3fb57bee0c3a9bcc6

openstack/cliff,dtroyer/cliff,openstack/cliff,dtroyer/cliff