Dedupe MFA requirements in chapter V2 and update text

[tghosth]

This Pull Request relates to issue #2587

[tghosth]

@elarlang ready for review :)

[tghosth]

(converted to draft to prevent accidental merge)

[elarlang]

First I have question:

• 2.7.3 - maybe it is easier when this "once" stays in this requirement?

Tags to correct:

• 2.6.1 - covers 2.2.6, but 2.2.6 does not have matching tag "covered by 2.6.1" (2.8.4 is not updated to 2.6.1)
• 2.6.5 - modified, moved from (not added)
• 2.8.4 - deleted, merged to
• 2.8.3 - deleted, merged to

[tghosth]

First I have question:

* 2.7.3 - maybe it is easier when this "once" stays in this requirement?

Tags to correct:

* 2.6.1 - covers 2.2.6, but 2.2.6 does not have matching tag "covered by 2.6.1" (2.8.4 is not updated to 2.6.1)

* 2.6.5 - modified, moved from (not added)

* 2.8.4 - deleted, merged to

* 2.8.3 - deleted, merged to

Fixed tags and responded to your question here: #2587 (comment)

[tghosth]

@elarlang are you ready to approve this now?

[jmanico]

This is going to collide with my "remove ETC" PR - but that is ok. Your PR is way more complex and I can adjust my branch after this is perged.