Drop datrie support

[gsnedders]

see #442

[codecov-commenter]

Codecov Report

Merging #455 into master will increase coverage by 0.30%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #455      +/-   ##
==========================================
+ Coverage   90.60%   90.90%   +0.30%     
==========================================
  Files          50       49       -1     
  Lines        6983     6930      -53     
  Branches     1328     1322       -6     
==========================================
- Hits         6327     6300      -27     
+ Misses        497      471      -26     
  Partials      159      159              

Impacted Files	Coverage Δ
html5lib/_trie/__init__.py	100.00% <100.00%> (ø)
html5lib/_inputstream.py	91.77% <0.00%> (-0.15%)	⬇️
html5lib/html5parser.py	98.44% <0.00%> (+1.19%)	⬆️

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[gsnedders]

Landed given no review forthcoming in three months.