Fix imports and general cleanup

· Import from compat what comes from compat. Yes, some names are available in utils too, but that's an implementation detail.
· Use _match_id consistently whenever possible
· Fix some outdated tests
· Use consistent valid URL (always match the whole protocol, no ^ at start required)
· Use modern test definitions

youtube_dl/swfinterp.py

@@ -4,8 +4,8 @@ import collections
 import io
 import zlib
 
+from .compat import compat_str
 from .utils import (
-    compat_str,
     ExtractorError,
     struct_unpack,
 )