Remove unicode character inserted into video_xfields

Fixes unicode character added with https://github.com/edx/edx-platform/commit/c1ef41fe6af55afa2c460ff2b4952401df6ab575#diff-828847f33fdd8417f882876864fcf359R82

Fixes this error:
```
File "/Users/sarina/edx_all/edx-platform/common/lib/xmodule/xmodule/video_module/video_xfields.py", line 82
SyntaxError: Non-ASCII character '\xe2' in file /Users/sarina/edx_all/edx-platform/common/lib/xmodule/xmodule/video_module/video_xfields.py on line 82, but no encoding declared; see http://www.python.org/peps/pep-0263.html for details
```