Don't linkify profs in section table on search page

Fixes #102

Currently there are broken links on the search page ("Explore courses") due
to #98. This is the simplest fix -- just don't link up those profs. Ideally,
we make those links look like '/course/econ101#l_smith' so that a user could
click directly to the prof review on the course details page, but due to the
way we async-load prof reviews, this won't actually work.

Search page:

![image](https://f.cloud.github.com/assets/159687/2307194/d853aec8-a2a2-11e3-8aff-1037ab5f7c2d.png)

Details page:

![image](https://f.cloud.github.com/assets/159687/2307201/ebd99da4-a2a2-11e3-95c1-46937bb36d69.png)