Remove out of date references to linuxcontainers.org in stable-5.0 branch

[tomponline]

I noticed that due to the large structural changes that have occurred in the docs between the 5.0 and main branches that most doc commits cannot be cherry-picked.

As such there are still out of date mentions of linuxcontainers.org in the docs.

We should review those and update/remove where appropriate.

[tomponline]

@ru-fu did this get done in the end?

[ru-fu]

Not yet, no. :( Tracked in Jira LXD-844.

[simondeziel]

Fixed by #14202