Clean up licenses of qtcluster snippets

qtdoc/doc/src/snippets/qtcluster contains a few files with non-unified license headers:

designerImports/ClusterDemo/plugin.cpp:** $QT_BEGIN_LICENSE:LGPL$
etcprovider.h:** $QT_BEGIN_LICENSE:LGPL21$
qml/CarModelMain.qml:** $QT_BEGIN_LICENSE:LGPL3$
qml/CarModelSports.qml:** $QT_BEGIN_LICENSE:LGPL3$
qml/CarViewElectric.qml:** $QT_BEGIN_LICENSE:LGPL3$
qml/CarViewSports.qml:** $QT_BEGIN_LICENSE:LGPL3$
qml/dash_hybrid/CenterViewCalendar.qml:** $QT_BEGIN_LICENSE:GPL-QTAS$
qml/dash_hybrid/CenterViewCarInfo.qml:** $QT_BEGIN_LICENSE:GPL-QTAS$
qml/dash_hybrid/CenterViewContacts.qml:** $QT_BEGIN_LICENSE:GPL-QTAS$
qml/dash_hybrid/CenterViewMusic.qml:** $QT_BEGIN_LICENSE:GPL-QTAS$
qml/dash_hybrid/DashboardView.qml:** $QT_BEGIN_LICENSE:LGPL3$
qtiviclusterdata.cpp:** $QT_BEGIN_LICENSE:LGPL3-PELAGICORE$
qtiviclusterdata.h:** $QT_BEGIN_LICENSE:LGPL3-PELAGICORE$

These should arguably all be BSD .