Confusing feature attributes

In https://gitlab.com/gitlab-com/www-gitlab-com/blob/a928516e3787ecca4fa207c6260c798dd82f627c/data/features.yml#L1649 we have:

    gitlab_com: false
    not_on_gitlab_com: true
    gitlab_self_hosted: true
    gitlab_ci: true

of these on not_on_gitlab_com is documented on https://gitlab.com/gitlab-com/www-gitlab-com/blob/master/doc/features.md

I propose to remove all three other attributes.

mentioned in issue #1568

We need the following for the comparison pages:

gitlab_com: false
gitlab_self_hosted: true
gitlab_ci: true

They're partly documented in https://gitlab.com/gitlab-com/www-gitlab-com/blob/df72d04f481f5d213010d782932e7223e769dece/doc/features.md#create-or-update-the-comparison-pages-under-comparison, and by partly I mean implied. Maybe we can be more explicit what is used in the comparison pages and what not.

Actually, the possible attributes are the ones listed in the table, plus all attributes under product_one, product_two.

I think:

1. We need to better document all possible attributes explicitly.
2. Rename one, some or all of gitlab_com, not_on_gitlab_com, gitlab_self_hosted to be more descriptive.

Actually, gitlab_self_hosted is not used anywhere, I think we removed the comparison page altogether at some point. I'll remove it

assigned to @axil and unassigned @connorshea

mentioned in merge request !7377 (merged)

changed milestone to %10.0

added features label

closed via merge request !7377 (merged)

mentioned in commit 2ed4716b