Remove CentOS 5.9 from kitchen.yml

The trac package in CentOS 5.9 from EPEL is too old.

From the TracAdmin wiki page, referring to pre-0.11 versions (EPEL for
5.9 has 0.10):

"Note that in version 0.11 of Trac, initenv lost an extra last argument
<templatepath>, which was used in previous versions to point to the
templates folder. If you are using the one-liner 'trac-admin
/path/to/trac/ initenv <projectname> <db> <repostype> <repospath>' in
the above and getting an error that reads 'Wrong number of arguments
to initenv: 4', then this is because you're using a trac-admin script
from an older version of Trac. "

http://trac.edgewall.org/wiki/TracAdmin