return value would not be a valid array when json encoded after unlink().

fixes #6065

feature is not reliable

fixes #5136

do not use scripting as it is disabled by default and will cause edge
case queries to fail

fixes #4187

fixes #3587

issue #3520

breaking changes.

better not delete all to avoid data loss

pr #2324

```
$result = Article::find()->query(["field" => ["title" => "yii"]])->all();
````

fixes #1993

meet the AR interface requirements.