Deletes created files, database tables, and reverts all environment changes.
This method needs to be invoked for both unit and integration tests.
Overrides TestBase::tearDown
TestBase::prepareDatabasePrefix()
TestBase::changeDatabasePrefix()
TestBase::prepareEnvironment()
function tearDown() {
// Revert $_GET.
$_GET = $this->GET;
parent::tearDown();
}