[DOC] Add bounds to sphinx requirement

As ONAP was created before Oct 20 2020 in RTD, we
must set bounds to enforce a compatible Sphinx version
(see manual).

It also removes useless deps and incorrect concrete deps.

Issue-ID: DOC-782

Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
Change-Id: I83e36d4ff783b5b6b133abe700a55803fc930aaa
(cherry picked from commit ace2a55c8d5c41de90f00162b45856870ad04c5d)
2 files changed