Drop evince browser plugin
Since epiphany no longer officially supports NPAPI plugins as of 3.29, I think it's time for evince to drop the code for its browser plugin.
Given how late we are in the release cycle, maybe it would be best to change the default so that the browser plugin isn't build for 3.30. And then early in the 3.31 cycle, drop the code.
cc/ @mcatanzaro