Android: add comment to remove unused private methods in Qt 7

These methods don't seem to be used by anyone now, but not sure
how it was before, so to not run into any BiC issues, just add
a comment to remove them in Qt 7.

Change-Id: Ie30a3d2adcbbb7530d9cf72f03b78ecfa06e426c
Reviewed-by: Ville Voutilainen <ville.voutilainen@qt.io>

src/corelib/kernel/qjniobject.h

@@ -436,12 +436,13 @@ private:
     void callVoidMethodV(JNIEnv *env, jmethodID id, ...) const;
     // ### Qt 7: merge into ... overload
     void callVoidMethodV(JNIEnv *env, jmethodID id, va_list args) const;
+    // ### Qt 7: remove unused
     QJniObject callObjectMethodV(const char *methodName, const char *signature,
                                  va_list args) const;
-
+    // ### Qt 7: remove unused
     static QJniObject callStaticObjectMethodV(const char *className, const char *methodName,
                                               const char *signature, va_list args);
-
+    // ### Qt 7: remove unused
     static QJniObject callStaticObjectMethodV(jclass clazz, const char *methodName,
                                               const char *signature, va_list args);