Issue 35036: logger failure in suspicious.py

There were some recent changes made in ee171a26c11 to fix Sphinx related deprecation warnings. During the change self.info() was changed to self.logger.info() . Logger expects a positional argument that contains the message thus causing failure. I think empty string can be passed here. I changed it back to self.info() and ran `make suspicious` locally and it only printed deprecation warning. Looking the source the previous method had message default to '' thus self.info() was working.

def info(self, message='', nonl=False):
    # type: (unicode, bool) > None
    """Emit an informational message.

    If *nonl* is true, don't emit a newline at the end (which implies that
    more info output will follow soon.)

    .. deprecated:: 1.6
       Use :mod:`sphinx.util.logging` instead.
    """
    warnings.warn('app.info() is now deprecated. Use sphinx.util.logging instead.',
                  RemovedInSphinx20Warning)
    logger.info(message, nonl=nonl)


Sample failure : https://travis-ci.org/python/cpython/jobs/444263040#L560

I am adding @pablogsal for thoughts on the fix. I will add a PR shortly.