[autotests] Drop KWIN_TEST_MAIN macro

It was not doing anything in addition and the documentation was
completely wrong as it does the same thing as QTEST_MAIN.

autotests/test_client_machine.cpp

@@ -151,5 +151,5 @@ void TestClientMachine::emptyHostName()
     QCOMPARE(spy.isEmpty(), false);
 }
 
-KWIN_TEST_MAIN(TestClientMachine)
+QTEST_MAIN(TestClientMachine)
 #include "test_client_machine.moc"

autotests/test_xcb_size_hints.cpp

@@ -371,5 +371,5 @@ void TestXcbSizeHints::geometryHintsBeforeRead()
     QCOMPARE(hints.windowGravity(), XCB_GRAVITY_NORTH_WEST);
 }
 
-KWIN_TEST_MAIN(TestXcbSizeHints)
+QTEST_MAIN(TestXcbSizeHints)
 #include "test_xcb_size_hints.moc"

autotests/test_xcb_window.cpp

@@ -207,5 +207,5 @@ void TestXcbWindow::destroyNotManaged()
     QVERIFY(attribs);
 }
 
-KWIN_TEST_MAIN(TestXcbWindow)
+QTEST_MAIN(TestXcbWindow)
 #include "test_xcb_window.moc"

autotests/test_xcb_wrapper.cpp

@@ -525,5 +525,5 @@ void TestXcbWrapper::testMotif()
     QTEST(hints.close(), "expectedClose");
 }
 
-KWIN_TEST_MAIN(TestXcbWrapper)
+QTEST_MAIN(TestXcbWrapper)
 #include "test_xcb_wrapper.moc"

autotests/testutils.h

@@ -24,14 +24,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 // XCB
 #include <xcb/xcb.h>
 
-// like QTEST_MAIN, just using a QApplication for X11 interaction
-#define KWIN_TEST_MAIN(TestObject) \
-int main(int argc, char *argv[]) { \
-    QApplication app(argc, argv); \
-    TestObject tc; \
-    return QTest::qExec(&tc, argc, argv); \
-}
-
 namespace KWin {
 
 /**