fontc promotes some subtables that fontmake does not

This is probably something we could normalize, although it is nice to know that we're doing it means we're generating slightly less efficient binary.

```
python3 -m ttx_diff 'https://github.com/Vectro-Type-Foundry/kablammo?cccc120d23#sources/Kablammo.glyphs'
```

Start by running the provided `python3 -m ttx_diff` command against the Kablammo source and compare the fontc and fontmake outputs. Trace which subtables are promoted differently, then confirm the behavior is normalized and the resulting binary is no less efficient.

Written by the indexing model from the issue text.