Remove Open Source and ENterprise from the top menu

[tzach]

Starting from 2025.1, there is no need to link to Open Source and Enterprise
Only to https://docs.scylladb.com/manual/stable/

[annastuchlik]

This is already fixed with #1376.
It's being distributed with the 1.8.6 Sphinx theme, and it's already applied in some repos.
In the Manual docs, it will be available when this PR is merged: scylladb/scylladb#23537