Remove quartz CGGLContext

[corranwebster]

Fixes #514. Requires #513 since CI won't get to this point without that change.

[codecov-io]

Codecov Report

Merging #515 (cdb0705) into master (22cdf49) will increase coverage by 4.45%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #515      +/-   ##
==========================================
+ Coverage   30.71%   35.16%   +4.45%     
==========================================
  Files         210      210              
  Lines       17840    17840              
  Branches     2454     2454              
==========================================
+ Hits         5479     6274     +795     
+ Misses      12028    11161     -867     
- Partials      333      405      +72     

Impacted Files	Coverage Δ
enable/null/image.py	0.00% <0.00%> (-85.72%)	⬇️
enable/component_editor.py	78.72% <0.00%> (-4.26%)	⬇️
enable/colors.py	39.56% <0.00%> (-3.30%)	⬇️
kiva/trait_defs/kiva_font_trait.py	79.68% <0.00%> (-3.13%)	⬇️
enable/tools/hover_tool.py	74.24% <0.00%> (-3.04%)	⬇️
enable/api.py	93.93% <0.00%> (ø)
kiva/fonttools/font_manager.py	56.41% <0.00%> (+0.61%)	⬆️
enable/component.py	55.29% <0.00%> (+0.64%)	⬆️
kiva/fonttools/font.py	50.00% <0.00%> (+3.94%)	⬆️
kiva/gl.py	34.91% <0.00%> (+34.91%)	⬆️
... and 10 more

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[jwiggins]

LGTM