doc: Remove reference to QWaylandView from QML docs

This amends 3360877df04358df6f1b992af27f892e52b616ad.

The QWaylandView has no equivalent in QML, so the
statement that a QWaylandQuickItem represents a
QWaylandView does not add any information and can be
confusing.

In addition, it is more of a technical detail than an
actual description of what the class does even for C++,
and users would have to click the link to QWaylandView
to understand the purpose of the class.

Therefore, this updates both C++ and QML docs to remove
the reference to the QWaylandView class.

Pick-to: 6.12
Change-Id: Icff8d04079d8a7b2782ddd95f00df5dda42d71e9
Reviewed-by: Bernd Weimer <bernd.weimer@qt.io>