[COOK-4095] remove explicit ref to libpq-dev package

There is no libpq-dev package on RedHat 6 (maybe other versions too).

There is already code which installs client packages - this is supposed
to deal with installing postgresql devel packages.
[COOK-4147] add oracle rpms in default['postgresql']['pgdg']['repo_rpm_url']
Merge branch 'COOK-4147' - add oracle entry for yum rpms