JERSEY-1535: Disable harmful, half-baked JSON-P support

JSON-P support currently corrupts JavaScript responses; this pull-requests simply removes it (temporarily).

I'm working on fixing the feature, I'll do a pull-request when I get it working in an acceptable way, but I have no idea when I'll get to that point so in the mean time removing it is the bare minimum (IMO) before shipping 2.0 GA.

(I can't remember if I signed the OCA, but maybe it's not needed here as I'm not really _contributing_ anything…)