fix up imports

youtube_dl/extractor/generic.py

@@ -12,6 +12,7 @@ from ..utils import (
     compat_urlparse,
     compat_xml_parse_error,
 
+    determine_ext,
     ExtractorError,
     float_or_none,
     HEADRequest,

youtube_dl/extractor/musicvault.py

@@ -1,11 +1,9 @@
 from __future__ import unicode_literals
 
-import json
 import re
 
 from .common import InfoExtractor
 from ..utils import (
-    strip_jsonp,
     parse_duration,
     unified_strdate,
 )

youtube_dl/extractor/ustream.py

@@ -1,6 +1,5 @@
 from __future__ import unicode_literals
 
-import json
 import re
 
 from .common import InfoExtractor