Remove Azure backend, update dependencies

[bensteinberg]

By removing the Azure backend and updating pyopenssl, I was able to update cryptography:

https://cryptography.io/en/latest/changelog/#v43-0-1

https://www.pyopenssl.org/en/latest/changelog.html

Removing the Azure backend meant undoing both #2695 and #3208 fwiw.

@mcharters thanks for your comments on #3104. If you do choose to update your fork, you'll find that there have been very significant changes -- if you try it, and want advice about setting up the new capture system, please let us know.

[rebeccacremona]

👍

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.84%. Comparing base (58402b0) to head (b70124e).
Report is 4 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3597      +/-   ##
===========================================
+ Coverage    68.81%   68.84%   +0.02%     
===========================================
  Files           48       48              
  Lines         7014     7004      -10     
===========================================
- Hits          4827     4822       -5     
+ Misses        2187     2182       -5     

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