Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Remove jjb-sandbox as we now have jjb-deploy"
  - Remove jjb-sandbox as we now have jjb-deploy

    Now that the sandbox is available and we can easily deploy jobs using
    'jjb-deploy' or upload them through the cli, this outdated directory can
    be removed.

    Change-Id: I680dbc84eeba140adac7b69ea0af4ed26d160362
    Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index d12b7f9..3a55ac0 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit d12b7f95de23d0732956fa302dec69324d409752
+Subproject commit 3a55ac00622a0a0d18d619805fea66767a75cfb4