Overlapping components don't get merged in static ttf

We just noticed while dealing with [League Spartan](https://github.com/emmamarichal/league-spartan)

In static ttf, overlapping components are decomposed but outline don't get merged (and so they overlap). If static ttf have merged contours by default, so decomposed components should too, right?

Building process uses gftools builder with direct source as argument. Before and after export:

cc @emmamarichal (who is currently working with me to onboard fonts in Google Fonts)