No need to create a storage within remove

Potential fix for
````
Doctrine\DBAL\DBALException: An exception occurred while executing 'SELECT lastval()':

SQLSTATE[55000]: Object not in prerequisite state: 7 ERROR: lastval is not yet defined in this session in /home/travis/build/owncloud/core/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/DBALException.php on line 47

Call Stack:

0.0013 379928 1. {main}() /home/travis/.phpenv/versions/5.4.27/bin/phpunit:0
0.0222 878232 2. PHPUnit_TextUI_Command::main() /home/travis/.phpenv/versions/5.4.27/bin/phpunit:583
0.0223 884424 3. PHPUnit_TextUI_Command->run() phar:///home/travis/.phpenv/versions/5.4.27/bin/phpunit/phpunit/TextUI/Command.php:132
1.2410 65654488 4. PHPUnit_TextUI_TestRunner->doRun() phar:///home/travis/.phpenv/versions/5.4.27/bin/phpunit/phpunit/TextUI/Command.php:179
3.7950 66563152 5. PHPUnit_Framework_TestSuite->run() phar:///home/travis/.phpenv/versions/5.4.27/bin/phpunit/phpunit/TextUI/TestRunner.php:425
310.3150 143034232 6. PHPUnit_Framework_TestSuite->run() phar:///home/travis/.phpenv/versions/5.4.27/bin/phpunit/phpunit/Framework/TestSuite.php:675
310.7059 143393552 7. call_user_func:{phar:///home/travis/.phpenv/versions/5.4.27/bin/phpunit/phpunit/Framework/TestSuite.php:680}() phar:///home/travis/.phpenv/versions/5.4.27/bin/phpunit/phpunit/Framework/TestSuite.php:680
310.7059 143393552 8. Test_Files_Sharing_Base::tearDownAfterClass() phar:///home/travis/.phpenv/versions/5.4.27/bin/phpunit/phpunit/Framework/TestSuite.php:680
310.7106 143390688 9. OC_User::deleteUser() /home/travis/build/owncloud/core/apps/files_sharing/tests/base.php:95
310.7127 143389752 10. OC\Files\Cache\Storage::remove() /home/travis/build/owncloud/core/lib/private/user.php:213
310.7127 143389976 11. OC\Files\Cache\Storage->__construct() /home/travis/build/owncloud/core/lib/private/files/cache/storage.php:86
310.7134 143390664 12. OC_DB::insertid() /home/travis/build/owncloud/core/lib/private/files/cache/storage.php:42
310.7134 143390664 13. OC\DB\Connection->lastInsertId() /home/travis/build/owncloud/core/lib/private/db.php:251
310.7134 143390752 14. OC\DB\AdapterPgSql->lastInsertId() /home/travis/build/owncloud/core/lib/private/db/connection.php:145
310.7134 143390840 15. Doctrine\DBAL\Connection->fetchColumn() /home/travis/build/owncloud/core/lib/private/db/adapterpgsql.php:14
310.7134 143391024 16. OC\DB\Connection->executeQuery() /home/travis/build/owncloud/core/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php:408
310.7134 143391296 17. Doctrine\DBAL\Connection->executeQuery() /home/travis/build/owncloud/core/lib/private/db/connection.php:107