tst_QFactoryLoader: remove unused member variable

Commit 862f42e806 removed the last use
of the Android-only `directory` member, but didn't remove the member's
definition.

Remove it now, probably fixing a Clang -Wunused-private-field warning
on Android.

Pick-to: 6.6 6.5 6.2
Task-number: QTBUG-87438
Change-Id: I67a1d97f29a0dde20ff29fb9b5bbaa5611cb9e17
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

tests/auto/corelib/plugin/qfactoryloader/tst_qfactoryloader.cpp

@@ -19,10 +19,6 @@ class tst_QFactoryLoader : public QObject
 {
     Q_OBJECT
 
-#ifdef Q_OS_ANDROID
-    QSharedPointer<QTemporaryDir> directory;
-#endif
-
     QString binFolder;
 public slots:
     void initTestCase();