[5.5] Fix Database Collection Fresh for deleted records

[deleugpn]

When requesting a fresh() database collection, if any item has been deleted in a way that the collection itself is not aware, fresh() will fail with undefined offset

1) Illuminate\Tests\Integration\Database\EloquentCollectionFreshTest::test_eloquent_collection_fresh
ErrorException: Undefined offset: 1

/var/www/forks/framework/src/Illuminate/Database/Eloquent/Collection.php:162
/var/www/forks/framework/src/Illuminate/Support/Collection.php:833
/var/www/forks/framework/src/Illuminate/Database/Eloquent/Collection.php:134
/var/www/forks/framework/src/Illuminate/Database/Eloquent/Collection.php:163
/var/www/forks/framework/tests/Integration/Database/EloquentCollectionFreshTest.php:53

The problem is because $model->exists will only return false if we use the same collection to delete the records. When deleting the records without the collection's knowledge, $model->exists will still return true, but $freshModels will not have that record.

[deleugpn]

I really needed this fix on 5.4