Stop using contrib

[amalloy]

I discovered we're using c.c.json as well as c.c.prxml (the latter I knew about). With 1.3 released, we should be making some effort to eliminate our contrib dependencies. prxml we can replace as soon as data.xml has a released version, but nobody seems to be trying to make that happen, so who knows. The hard part, of course, is avoiding transitive dependencies on contrib, but we should start by removing our direct dependency.