Swift: remove parameter labels from function types

As discussed [in this accepted proposal][1], parameter labels do not
take part any more in making up a function type, so we need to not
extract them any more to avoid DB inconsistencies.

These were unused in the library, which makes the upgrade and downgrade
scripts have full compatibility.

[1]: 9c53790a13/proposals/0111-remove-arg-label-type-significance.md

swift/schema.py

@@ -949,7 +949,6 @@ class TypeRepr(AstNode):
 class AnyFunctionType(Type):
     result: Type
     param_types: list[Type]
-    param_labels: list[optional[string]]
     is_throwing: predicate | doc("this type refers to a throwing function")
     is_async: predicate | doc("this type refers to an `async` function")