Qnx: Avoid use of QtcProcess::ioDevice()

And drop the function from the QtcProcess interface, as this was the
only user.

Change-Id: I5a21cdaacb3f91f78058e80cbe1cb1572e9bf331
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/libs/utils/qtcprocess.cpp

@@ -779,11 +779,6 @@ QString QtcProcess::exitMessage()
     return QString();
 }
 
-QIODevice *QtcProcess::ioDevice()
-{
-    return d->m_process;
-}
-
 QByteArray QtcProcess::allRawOutput() const
 {
     if (!d->m_stdOut.rawData.isEmpty() && !d->m_stdErr.rawData.isEmpty()) {