FileField needlessly serializes upload_to; same problems with some other fields

[Roman Odaisky]

django.db.models.fields.FileField explicitly includes upload_to in the serialization process. This takes no part in the actual migration process but causes errors if the value of the field is a lambda function. Instead, the deconstruct() functions for FileField and other fields should only serialize arguments relevant to subsequent ALTER commands issued to the DBMS.

Other places where this problem arises include ForeignKey.limit_choices_to — do changes to this attribute mandate a new migration and is it appropriate to have it fail if the value is a lambda?

Once fixed, #22351 can be reverted.