Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  to dc3f6df1a30f07e3205e62092a0d7301dacdaf8c
  - Remove failing functest-rtd-jobs

    This job always fails (missing python interpreter) [1] and it's
    useless as Functest team manages its docs on readthedocs.

    It's worth mentioning that opnfvdocs load Functest docs as a submodule.

    [1] https://build.opnfv.org/ci/job/functest-rtd-verify-master/73/

    Change-Id: I8f0180a6befa80e96b9d393b2c3ac627bdb278c5
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>