Change configure license

According to QUIP-18 [1], all build system files should be
BSD-3-Clause

[1]: https://contribute.qt-project.org/quips/18

Task-number: QTBUG-121787
Change-Id: I88e3640b32e6b4bd83c49c14df6aecd7c824aef7
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
(cherry picked from commit 35fbb65)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

configure

@@ -1,7 +1,7 @@
 #!/bin/sh
 # Copyright (C) 2016 The Qt Company Ltd.
 # Copyright (C) 2016 Intel Corporation.
-# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+# SPDX-License-Identifier: BSD-3-Clause
 
 #-------------------------------------------------------------------------------
 # script initialization