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· Fix some outdated tests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/downloader/http.py

@@ -4,11 +4,12 @@ import os
 import time
 
 from .common import FileDownloader
-from ..utils import (
+from ..compat import (
     compat_urllib_request,
     compat_urllib_error,
+)
+from ..utils import (
     ContentTooShortError,
-
     encodeFilename,
     sanitize_open,
     format_bytes,