feat: remove spdy

[bjohansebas]

Summary

I’ve just confirmed that Express still doesn’t work properly with HTTP/2, seemingly due to finalhandler (I’ll need to investigate it further). So this PR only removes support for spdy. Hopefully I’ll be able to get Express working with HTTP/2 soon, but until then we should recommend using a custom server.

What kind of change does this PR introduce?

Did you add tests for your changes?

Does this PR introduce a breaking change?

If relevant, what needs to be documented once your changes are merged or what have you already documented?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.66%. Comparing base (873a803) to head (6f98e9c).

Additional details and impacted files

@@            Coverage Diff             @@
##             next    #5635      +/-   ##
==========================================
+ Coverage   83.62%   83.66%   +0.04%     
==========================================
  Files          11       11              
  Lines        1954     1947       -7     
  Branches      729      723       -6     
==========================================
- Hits         1634     1629       -5     
+ Misses        287      285       -2     
  Partials       33       33              

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