Remove widgets config test.

Since it's not guaranteed that other Qt modules will be built by the
time qmake is run (and config.tests are created) we can't rely on
compilation.  Just check the module.pri variable for widgets instead.

Change-Id: I352cf6427b748b89b69ec17588ce0dd83065090f
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>

src/plugins/gstreamer/gstreamer.pro

@@ -5,7 +5,7 @@ TARGET = qgstengine
 QT += multimedia-private network
 CONFIG += no_private_qt_headers_warning
 
-contains(config_test_widgets, yes) {
+!isEmpty(QT.widgets.name) {
     QT += widgets multimediawidgets-private
     DEFINES += HAVE_WIDGETS
 }
@@ -46,7 +46,7 @@ maemo6 {
 
     PKGCONFIG += qmsystem2
 
-    isEqual(QT_ARCH,armv6):contains(config_test_widgets, yes) {
+    isEqual(QT_ARCH,armv6):!isEmpty(QT.widgets.name) {
         HEADERS += qgstreamergltexturerenderer.h
         SOURCES += qgstreamergltexturerenderer.cpp
         QT += opengl
@@ -74,7 +74,7 @@ SOURCES += \
     gstvideoconnector.c \
 
 
-contains(config_test_xvideo, yes):contains(config_test_widgets, yes): {
+contains(config_test_xvideo, yes):!isEmpty(QT.widgets.name): {
     DEFINES += HAVE_XVIDEO
 
     LIBS += -lXv -lX11 -lXext