ari: Remove support for specifying channel vars during origination.

ari: Remove support for specifying channel vars during origination.

When we added support for specifying channel variables for an
origination, we didn't consider how that would interact with another
feature, namely specifying request parameters in a JSON request body.

The method of specifying channel variables (as a flat JSON object passed
in the JSON body) interferes with parsing parameters out of the request
body.

Unfortunately, fixing this would be a backward incompatible change. In
the interest of keeping the API sane and keeping our release schedule,
we're dropping the feature for specifying channel variables in the
origination request.

We will bring the feature back soon, as a backward compatible addition
to the API.

(closes issue ASTERISK-23051)
Review: https://reviewboard.asterisk.org/r/3088

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/12@404509 65c4cc65-6c06-0410-ace0-fbb531ad65f3