Don't include certificate info message templ for unavailable cert status

[bryanlandia]

This duplicates a change made to edx-platform in the base _dashboard_course_listing.html template. Here's that PR (currently merged to appsembler/ficus/develop)
appsembler/edx-platform#199

A previous PR to edx-platform changed the default certificate status for open-ended courses (courses with no end date) to 'unavailable', instead of 'processing'. This got rid of the confusing message 'Final course details are being wrapped up' under the course listing on the dashboard. This goes one step further and makes sure open-ended courses that have not been completed don't produce any kind of cert. message on the dashboard. Basically, this just gets rid of a styled grey

with no contents under each course (see screenshot).

I may want to refactor this one for Ginkgo, onward. There's a comment in the code about that.

[bryanlandia]

I realized my change in edx-platform would not take effect because of this this theme template override. I'm hoping to get this pushed out to at least one prod instance next week before my vacation Feb 15, so I'd appreciate a quick look @melvinsoft @grozdanowski ~~~thanks!~~