xcb: cleanup gl_integrations_plugin_base.pri

The original version (8758f532ae) of
this file was full of things that are irrelevant for XCB GL plugins.
Most of this has been cleaned out as side effect of porting to the
new configure system. This patch cleans up the remaining pieces.

It does not matter for XCB GL plugins if Qt was configured with
-qt-xcb or -system-xcb as those are dependencies of xcb_qpa_lib-private
and are not used directly by these plugins.

The only XCB dependencies that are directly used by these plugins
are libxcb-glx and libxcb, which are managed directly in xcb_glx.pro:

qtConfig(xcb-glx): QMAKE_USE += xcb_glx

Change-Id: I2175185902bb028de142c8ff6e0b0a3b76a09703
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>

src/plugins/platforms/xcb/gl_integrations/gl_integrations_plugin_base.pri

@@ -5,10 +5,3 @@ INCLUDEPATH += $$PWD/../
 
 load(qt_build_paths)
 
-!qtConfig(system-xcb) {
-    QMAKE_USE += xcb-static xcb
-} else {
-    qtConfig(xkb): QMAKE_USE += xcb_xkb
-    qtConfig(xcb-render): QMAKE_USE += xcb_render
-    QMAKE_USE += xcb_syslibs
-}