authz_groupfile/authz_user: don't log at ERROR for AUTHZ_DENIED, since
authz_core is collecting providers results. Subsequently reported in PR55523?

trunk patch: http://svn.apache.org/r1517366

Submitted by: covener
Reviewed by: jim, humbedooh


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1523267 13f79535-47bb-0310-9956-ffa450edef68