Android: Remove gradle.properties file handling

The modification of gradle.properties files was originally a feature of
the Android plugin which eventually moved over to androiddeployqt.

Moreover, this code got accidentally disabled in Qt Creator 4.10 and was
appartently not missed till now. I only noticed it while "FilePath-
ifying" code in the Andsroid plugin.

This change removes the gradle.properties file handling code from Qt
Creator.

Fixes: QTCREATORBUG-28494
Change-Id: Id4f2722f4965c877a065386b34a71d8368147b08
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

src/plugins/android/androidmanager.h

@@ -94,7 +94,6 @@ public:
                                          const QString &alias, const QString &certificatePasswd);
     static bool checkCertificateExists(const Utils::FilePath &keystorePath,
                                        const QString &keystorePasswd, const QString &alias);
-    static bool updateGradleProperties(ProjectExplorer::Target *target, const QString &buildKey);
 
     static QProcess *runAdbCommandDetached(const QStringList &args, QString *err = nullptr,
                                            bool deleteOnFinish = false);