Revert "Dap: avoid MissingIntPtrCtorException in DapInfoBar (bgo#722209)"

This reverts commit cdc919bcd61cb8b725ce995e9f9c66e5d80d202e.
GStreamerSharp: fix transcoding by using QueryCaps()

We were not using the same method of obtaining the caps as
the native backend, so go back to using QueryCaps().

Thanks go to Sebastian Dröge and Stephan Sundermann which
tracked this down (in irc://irc.freenode.net/#gstreamer).

(And to Bertrand Lorentz for reporting it.)