Remove requires from tests/core/case/database.php

When I run UnitTest, it returns error:

```
Warning: require_once(PHPUnit/Extensions/Database/TestCase.php): failed to open stream: No such file or directory in ***\tests\core\case\database.php on line 9

Fatal error: require_once(): Failed opening required 'PHPUnit/Extensions/Database/TestCase.php' (include_path='.;***\php\PEAR') in ***\tests\core\case\database.php on line 9
```

So I remove requires from this file, then it working fine.