Update and remove OAuth endpoints

[clarkbynum]

Updates based on https://developer.github.com/changes/2019-11-05-deprecated-passwords-and-authorizations-api/#authenticating-using-query-parameters

Fixes #1331.

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[codecov]

Codecov Report

Merging #1461 into master will increase coverage by 0.29%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1461      +/-   ##
==========================================
+ Coverage   67.72%   68.01%   +0.29%     
==========================================
  Files          94       94              
  Lines        8471     8389      -82     
==========================================
- Hits         5737     5706      -31     
+ Misses       1855     1821      -34     
+ Partials      879      862      -17

Impacted Files	Coverage Δ
github/github.go	89.77% <ø> (ø)	⬆️
github/authorizations.go	71.57% <100%> (+15.64%)	⬆️

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[clarkbynum]

@googlebot cla signed

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[gmlewis]

Thank you, @sh3nan1gans!
Apart from the missing custom media headers in the endpoints and the tests, this LGTM.

After these are added, we should be ready for a second review and LGTM before merging.

[clarkbynum]

Thanks for the quick turnaround @gmlewis ! I've added the custom media headers for the 4 endpoints you pointed (thanks for catching that by the way)
Please let me know if there's anything else that needs to be covered.

[gmlewis]

Thank you, @sh3nan1gans!
LGTM.

Awaiting second LGTM before merging.

[nightlark]

LGTM, fwiw

[gmlewis]

Thank you, @nightlark.
Merging.