[BrightcoveLegacy] mark test_BrightcoveLegacy_4 as gone

Black screen in browsers.

youtube-dl reports:
  [brightcove:legacy] ref:event-stream-356: Downloading webpage
  ERROR: brightcove said: This player is not enabled for access without key.

youtube_dl/extractor/brightcove.py

@@ -110,6 +110,7 @@ class BrightcoveLegacyIE(InfoExtractor):
                 'upload_date': '20140827',
                 'uploader_id': '710858724001',
             },
+            'skip': 'Video gone',
         },
         {
             # playlist with 'videoList'