When altering unique_together and removing a field, migrations may get wrong order.

[Curtis Maloney]

I just ran into a case where I was updating a model Trip, replacing one FK (owner) with another.
The model had an existing unique_together constraint including the old FK.

I'd written and applied migrations adding the new FK and setting its value.
When I created the migration to remove the old FK, the RemoveField was inserted _before_ the AlterUniqueTogether.

Since the field was removed first, the error comes:

django.core.exceptions.FieldDoesNotExist: Trip has no field named 'owner'

I fixed it by manually reordering the operations in the migration.

[Tim Graham]

Duplicate of #26180.