No prompt for backfill, double `RESET EXPRESSION` when changing from computed to hard required link

- EdgeDB Version: 4.7 and 5.3
- EdgeDB CLI Version: 5.1.0
- OS Version: macos

Steps to Reproduce:

Make the following change from computed to hard link. CLI doesn't prompt for a backfill expression for the link like it would when introducing a normal required - of course migration then fails if you have any data.

```esdl
module default {

type A {}

type B {
someA: A;
# required link a := assert_exists(.someA);
required link a: A;
}

}
```
```sh
$ edgedb migration create
did you alter link 'a' of object type 'default::B'? [y,n,l,c,b,s,q,?]
> l
The following DDL statements will be applied:
ALTER TYPE default::B {
ALTER LINK a {
RESET EXPRESSION;
RESET EXPRESSION;
RESET CARDINALITY;
SET TYPE default::A;
};
};
did you alter link 'a' of object type 'default::B'? [y,n,l,c,b,s,q,?]
> y
Created /Users/jack/dev/edgedbmay8/dbschema/migrations/00002-m1ybov2.edgeql, id: m1ybov226ukysh5hqbmjqjh47mtrpdnim7kkfpufplq5f6qv7tzziq
```