rng-tools: disable libjitterentropy support

libjitterentropy causes delays on reboot and shutdown.

Change-Id: I9d6c589750ac6bcbd67429836d3e7518da6b78dd
Reviewed-by: Mikko Gronoff <mikko.gronoff@qt.io>

meta-boot2qt-distro/recipes-support/rng-tools/rng-tools_%.bbappend

+############################################################################
+##
+## Copyright (C) 2019 The Qt Company Ltd.
+## Contact: https://www.qt.io/licensing/
+##
+## This file is part of the Boot to Qt meta layer.
+##
+## $QT_BEGIN_LICENSE:GPL$
+## Commercial License Usage
+## Licensees holding valid commercial Qt licenses may use this file in
+## accordance with the commercial license agreement provided with the
+## Software or, alternatively, in accordance with the terms contained in
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+############################################################################
+
+PACKAGECONFIG_remove = "libjitterentropy"