[doc] QCoreApplication::installTranslator() doesn't take ownership

Document it.

Pick-to: 6.3 6.2 5.15
Change-Id: I25d305945bf29348d6ea5756fbf80c418f812d0f
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/kernel/qcoreapplication.cpp

@@ -2113,6 +2113,8 @@ void QCoreApplicationPrivate::quit()
 
     The function returns \c true on success and false on failure.
 
+    \note QCoreApplication does \e not take ownership of \a translationFile.
+
     \sa removeTranslator(), translate(), QTranslator::load(), {Dynamic Translation}
 */