revert: use author-tools for idnits. (ietf-tools#4102) (ietf-tools#4116)

This reverts commit caf2227.

Author: rjsparks

ietf/settings.py

@@ -538,7 +538,7 @@ def skip_unreadable_post(record):
 # no slash at end
 IDTRACKER_BASE_URL = "https://datatracker.ietf.org"
 RFCDIFF_BASE_URL = "https://www.ietf.org/rfcdiff"
-IDNITS_BASE_URL = "https://author-tools.ietf.org/api/idnits"
+IDNITS_BASE_URL = "https://www.ietf.org/tools/idnits"
 XML2RFC_BASE_URL = "https://xml2rfc.tools.ietf.org/experimental.html"
 
 # The name of the method to use to invoke the test suite