Fix: Enable delete button for users with canDelete() but no canEdit() permissions

If a user has `canDelete()` permissions, but doesn't have `canEdit()` permissions, the 'Delete' button is disabled on the ItemEditForm, despite being enabled in the main GridField.

Cause: `$form->makeReadonly()` iterates over all fields/actions, disabling the 'delete' button even when the user has permission.