Clean up css operations

[tkh44]

What:

Why:

How:

Checklist:

• Documentation
• Tests
• Code complete

[codecov-io]

Codecov Report

Merging #175 into master will increase coverage by 0.36%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #175      +/-   ##
==========================================
+ Coverage   88.71%   89.08%   +0.36%     
==========================================
  Files          22       22              
  Lines         851      843       -8     
  Branches      222      219       -3     
==========================================
- Hits          755      751       -4     
+ Misses         72       70       -2     
+ Partials       24       22       -2

Impacted Files	Coverage Δ
src/glamor/clean.js	95.83% <100%> (-0.33%)	⬇️
src/glamor/CSSPropertyOperations/index.js	63.79% <100%> (ø)	⬆️
src/glamor/CSSPropertyOperations/CSSProperty.js	100% <100%> (ø)	⬆️
...lamor/CSSPropertyOperations/dangerousStyleValue.js	88.88% <100%> (+22.22%)	⬆️

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