Remove node-pngquant-native dependency

- Unnecessary native dependency
- It was disabled by default
- Has issues on certain platforms
- Not optimal for production use (performance)

publish.js

@@ -23,7 +23,6 @@ packageJson.name += '-light';
 packageJson.description = 'Map tile server for JSON GL styles - serving vector tiles';
 delete packageJson.dependencies['canvas'];
 delete packageJson.dependencies['@mapbox/mapbox-gl-native'];
-delete packageJson.dependencies['node-pngquant-native'];
 delete packageJson.dependencies['sharp'];
 
 delete packageJson.optionalDependencies;