Remove config deprecations and resolve compat

[ahopkins]

Removes the deprecated config methods from #1903, and resolves some compatibility with the old API.

[codecov]

Codecov Report

Merging #1999 (9a84a59) into master (7028eae) will decrease coverage by 0.56%.
The diff coverage is 29.54%.

@@            Coverage Diff             @@
##           master    #1999      +/-   ##
==========================================
- Coverage   92.02%   91.46%   -0.57%     
==========================================
  Files          30       29       -1     
  Lines        3323     3315       -8     
  Branches      579      580       +1     
==========================================
- Hits         3058     3032      -26     
- Misses        183      201      +18     
  Partials       82       82              

Impacted Files	Coverage Δ
sanic/utils.py	25.53% <11.42%> (-9.09%)	⬇️
sanic/config.py	100.00% <100.00%> (ø)

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[ahopkins]

Lots more unit testing needed here.

[ahopkins]

See #2007