doc(XCP-ng) Fix broken links in the XCP-ng documentation

[thomas-dkmt]

In the XCP-ng documentation, some links pointed to locations that were obsolete or just don't exist anymore (404 error, and some 503 errors).

• Wherever a more appropriate target location could be found, the links are now fixed.
• One dead link has been replaced by the actual, relevant content.
• Links where no substitute could be found have been removed.

[Fohdeesha]

So for the "Follow this (ignore steps 6 and 7, do not try to install the tools yet) https://support.citrix.com/article/CTX215427" line, I found a wayback copy of it, and all it's saying to do is delete two registry folders:

HKLM\SYSTEM\CurrentControlSet\Enum\XENBUS
HKLM\SYSTEM\CurrentControlSet\Enum\XENVIF

given half of the other steps in this list in our docu is also deleting registry keys, we can just put the two keys directly in a new line there, and get rid of the instruction line with this dead link

[dinhngtu]

Hi, I've created a PR with instructions for using XenClean (#326). That should replace the old instructions for removing old Citrix drivers.

[stormi]

Is the merge from master into this branch on purpose? If it is, we usually prefer a rebase of the PR branch over a merge commit.

[stormi]

There's a conflict with the master branch. You'll need to rebase on master (and solve the conflict in the process).