Make existing "dependencies" test optional in 2019-09

[handrews]

Since we reserve this keyword for compatibility (including in the default meta-schema), let's keep it around but move it to the optional section.

[Julian]

Hm -- is this really optional though?

Isn't the rename strictly for "preventing" downstream folks from redefining their own dependencies thing in their own vocabulary?

And so, isn't being able to reference arbitrary locations in a schema not in fact optional -- the fact that the place is called "dependencies" and happens to be the same place as a previous draft recommended is just a "coincidence"?

If the above understanding is correct it'd seem to me like if we do want to keep testing this that it should stay where it is, no?

[Julian]

Sorry, I somehow read this to be about definitions -- so never mind that last comment, but now I need to see what it means that we've kept this optional -- basically using it still applies the old behavior, but it's deprecated/discouraged essentially, or is it really optional that an implementation implements it? That'd sound a bit unfortunate to me if so, but need to read the spec I suppose.

[karenetheridge]

Those tests were removed in commit 960f519.