Remove some <py3.3 code

[andrewgsavage]

• Closes # (insert issue number)
• Executed pre-commit run --all-files with no errors
• The change is fully covered by automated unit tests
• Documented in docs/ as appropriate
• Added an entry to the CHANGES file

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.80%. Comparing base (64e7320) to head (9b63b19).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #250      +/-   ##
==========================================
+ Coverage   95.77%   95.80%   +0.03%     
==========================================
  Files          15       15              
  Lines        1916     1908       -8     
==========================================
- Hits         1835     1828       -7     
+ Misses         81       80       -1     

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[wshanks]

This looks fine to me. I had one question, but I am fine with merging if you prefer the way the code is now.

[newville]

+1 from me!