Fix explicit exports of pattern synonyms

[samuel-williams-da]

Before fixing explicit exports in data-deps, pattern synonyms in a module would be removed.
Now we try to explicitly export it and it doesn't exist.
We have 3 options:

• Fix this behaviour by filtering out exports of pattern syns
• Support pattern syns in data-deps
• Entirely drop pattern syns from the language

Remy prefers the last