Remove traces of Growl in QSystemTrayIcon code and documentation

Growl support was removed in Qt 5.8.

Change-Id: I00a36cd955194ca8ceee52841a89ca579da01284
Reviewed-by: Jake Petroules <jake.petroules@qt.io>

src/plugins/platforms/cocoa/qcocoasystemtrayicon.mm

@@ -72,8 +72,6 @@
 **
 ****************************************************************************/
 
-#define QT_MAC_SYSTEMTRAY_USE_GROWL
-
 #include "qcocoasystemtrayicon.h"
 
 #ifndef QT_NO_SYSTEMTRAYICON

src/widgets/util/qsystemtrayicon.cpp

@@ -107,9 +107,7 @@ static QIcon messageIcon2qIcon(QSystemTrayIcon::MessageIcon icon)
     \li All X11 desktop environments that implement the D-Bus
        \l{http://www.freedesktop.org/wiki/Specifications/StatusNotifierItem/StatusNotifierItem}
        specification, including recent versions of KDE and Unity.
-    \li All supported versions of \macos. Note that the Growl
-       notification system must be installed for
-       QSystemTrayIcon::showMessage() to display messages on \macos prior to 10.8 (Mountain Lion).
+    \li All supported versions of \macos.
     \endlist
 
     To check whether a system tray is present on the user's desktop,
@@ -399,9 +397,6 @@ bool QSystemTrayIcon::supportsMessages()
     On Windows, the \a millisecondsTimeoutHint is usually ignored by the system
     when the application has focus.
 
-    On \macos, the Growl notification system must be installed for this function to
-    display messages.
-
     Has been turned into a slot in Qt 5.2.
 
     \sa show(), supportsMessages()