Auth_Default: Remove unused loginFailed handler.

This patch removes the loginFailed handler in preparation for replacing it
with a new handler based on the exception handler code added to the
SimpleSAML_Auth_State class.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@1571 44740490-163a-0410-bde0-09ae8108e29a