Remove unavailable cloud vendors: auroracompute; InternetSolutions; dimension data

Summary

Adding support for all your cloud vendors and came across broken domains for:

• https://libcloud.readthedocs.io/en/stable/compute/drivers/auroracompute.html (which has a domain that is for sale)
• https://libcloud.readthedocs.io/en/stable/compute/drivers/internetsolutions.html (http://www.is.co.za site is down)
• https://libcloud.readthedocs.io/en/stable/compute/drivers/dimensiondata.html (redirects to ntt now which has two other vendors on libcloud already… I assume this company was bought by NTT)

Might be worth removing these vendors. (might update this issue with PRs and any other vendors that have disappeared)

In the past a user has already performed a significant clean up of old drivers, but it sounds like more work is needed and this is something which should evaluate and do a yearly basis or similar.

Feel free to open a PR with those changes.

FWIW, there are Aurora storage and DNS drivers (and corresponding documentation) that are also (most likely) defunct.

@aaron-sierra Sure thing; fixed that.

FYI: I intentionally did not remove dimensiondata properly as other vendors inherit from it.

@Kami - Can you merge that? - I also updated the website in https://github.com/apache/libcloud-site/pull/7