Remove obsolete uppercase_escape function

This function was only necessary with the old ajax format, which
was removed in 4d7bba92eb

Signed-off-by: Jesús <heckyel@hyperbola.info>

youtube/util.py

@@ -476,12 +476,6 @@ def update_query_string(query_string, items):
     return urllib.parse.urlencode(parameters, doseq=True)
 
 
-def uppercase_escape(s):
-    return re.sub(
-        r'\\U([0-9a-fA-F]{8})',
-        lambda m: chr(int(m.group(1), base=16)), s)
-
-
 def prefix_url(url):
     if url is None:
         return None