1131632 - Remove notes to disable SELinux in EL 5.

I put a lot of effort into making sure we can work with SELinux in
Enforcing mode in EL 5. We can, so this commit removes the documentation
that instructed users to disable it. It also recommends users to
re-enable it upon upgrading in the release notes.

https://bugzilla.redhat.com/show_bug.cgi?id=1131632