Silence 'make -s clean'.

* subversion/bindings/ctypes-python/setup.py
  (clean.run): Reduce the log level for not being able to remove
    a non-existent file.  (There is a similar case in distutils itself.)

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1479323 13f79535-47bb-0310-9956-ffa450edef68