AppMainWindow::raise: Use Qt's activateWindow

The work around doesn't seem to be needed anymore. The case that
is described is a Creator hitting a breakpoint, but not being raised.
This works for me on both gnome and kde with this workaround removed.

Removing the workaround also fixes:

Task-number: QTCREATORBUG-13845
Change-Id: I4f751c701a17ee39679b951b9cf7d52a68552d9f
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>

src/libs/utils/utils.pro

@@ -3,17 +3,6 @@ QT += gui network
 include(../../qtcreatorlibrary.pri)
 include(utils-lib.pri)
 
-linux-* {
-    !isEmpty(QT.x11extras.name) {
-        QT += x11extras
-        CONFIG += x11
-        DEFINES += QTC_USE_QX11INFO
-    } else {
-        warning("x11extras module not found, raising the main window might not work. " \
-                "(The x11extras module is part of Qt 5.1 and later.)")
-    }
-}
-
 win32: LIBS += -luser32 -lshell32
 # PortsGatherer
 win32: LIBS += -liphlpapi -lws2_32