[#2162] Remove repetitive debug logging.

See issue: https://github.com/ckan/ckan/issues/2162

As a result of this change, the start-up debug log is reduced to this:
```
(ckan)vagrant@precise64:/vagrant/src/ckan$ stty echo; paster serve --reload $CKAN_INI
Starting subprocess with file monitor
2014-12-29 10:41:26,446 DEBUG [ckan.logic] check access - user None, action get_site_user
2014-12-29 10:41:26,447 DEBUG [ckan.logic] Access OK.
2014-12-29 10:41:26,467 DEBUG [ckan.plugins.core] Loading the synchronous search plugin

2014-12-29 10:41:28,743 DEBUG [ckan.logic] check access - user None, action get_site_user
2014-12-29 10:41:28,743 DEBUG [ckan.logic] Access OK.
2014-12-29 10:41:28,822 DEBUG [ckan.lib.app_globals] config `ckan.site_title` set to `CKAN` from config
2014-12-29 10:41:28,839 DEBUG [ckan.lib.app_globals] config `ckan.site_logo` set to `/base/images/ckan-logo.png` from config
2014-12-29 10:41:28,885 CRITI [ckan.lib.uploader] Please specify a ckan.storage_path in your config
                         for your uploads
Starting server in PID 4339.
serving on 0.0.0.0:5000 view at http://127.0.0.1:5000
```