QProcess: remove a XFAIL for QNX

91dcc76fc1 might have fixed the underlying issue, so we no longer
need the XFAIL codepath at all.

Fixes: QTBUG-114720
Change-Id: I67ccbed67a0536b679c50c26eb0b3e51c93dceeb
Pick-to: 6.6
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

tests/auto/corelib/io/qprocess/tst_qprocess.cpp

@@ -1807,10 +1807,6 @@ void tst_QProcess::unixProcessParameters()
     QVERIFY(process.waitForFinished(5000));
 
     const QString stdErr = process.readAllStandardError();
-#ifdef Q_OS_QNX
-    if (stdErr != QString())
-        QEXPECT_FAIL("ignore-sigpipe", "QTBUG-114720: flag is sometimes ignored", Abort);
-#endif
     QCOMPARE(stdErr, QString());
     QCOMPARE(process.readAll(), QString());
     QCOMPARE(process.exitCode(), 0);