contrib: drop Gluon version from CI site

Drop the Gluon version reference from the site configuration used for
the CI builds.

These version indicators were most likely just copied from the example
site in the docs, where the version information makes sense. However,
the CI site is always built for a specific Gluon version and therefor
commit.

This avoids editing the version for each release.

Signed-off-by: David Bauer <mail@david-bauer.net>

contrib/ci/minimal-site/site.conf

--- This is an example site configuration for Gluon v2023.2
+-- This is an example site configuration
 --
 -- Take a look at the documentation located at
 -- https://gluon.readthedocs.io/ for details.

contrib/ci/olsr-site/site.conf

--- This is an example site configuration for Gluon v2023.2
+-- This is an example site configuration
 --
 -- Take a look at the documentation located at
 -- https://gluon.readthedocs.io/ for details.