Doc: removed reference to sizeHint

sizeHint is not a property of QQuickView
Task-number: QTBUG-39044
Change-Id: I6e19e975ab71f73ddaf703956afb90f2e607b6f8
Reviewed-by: Martin Smith <martin.smith@digia.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>