urllib.request: Remove unused import (GH-5268)

Lib/urllib/request.py

@@ -1792,7 +1792,6 @@ def retrieve(self, url, filename=None, reporthook=None, data=None):
             if filename:
                 tfp = open(filename, 'wb')
             else:
-                import tempfile
                 garbage, path = splittype(url)
                 garbage, path = splithost(path or "")
                 path, garbage = splitquery(path or "")