Move uncurry transform to mini_c

This fixes bugs caused by uncurrying in commands like interpret, compile-storage, etc which operate with a file and a separate expression. Now uncurrying only happens on whole programs, so the bugs disappear.

It's also significantly simpler (e.g. no modules) and should become even simpler in future versions of mini_c.

It's essentially the same thing as the self_ast_typed version, just adapted to mini_c.

This depends on !1030 (merged) to avoid implementing E_let_tuple.