Remove unused variable, found by ICC 14

qxslttokenizer.cpp(700): warning #177: variable "val" was declared but never referenced
              const QStringRef val(m_currentAttributes.value(CommonNamespaces::XML, QLatin1String("space")));
                               ^

Change-Id: Ic806bf1e9c22ead8680907b0e22794d7b07dcc90
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>