[imdb] Remove test md5

They seem to reencode quite frequently, so simply remove the md5 sum.

youtube_dl/extractor/imdb.py

@@ -16,7 +16,6 @@ class ImdbIE(InfoExtractor):
 
     _TEST = {
         'url': 'http://www.imdb.com/video/imdb/vi2524815897',
-        'md5': '9f34fa777ade3a6e57a054fdbcb3a068',
         'info_dict': {
             'id': '2524815897',
             'ext': 'mp4',