Don't emit `@preconcurrency import` remarks when we're skipping function bodies
This eliminates spurious warnings suggesting that folks remove
`@preconcurrency` from imports that occur during `-emit-module` phases,
because we're skipping function bodies and, therefore, the code that
would depend on the `@preconcurrency` import.
Fixes https://github.com/apple/swift/issues/58183 / rdar://89940926.