This has a non-insignificant cost (since the size is at least 260 bytes)
in renderers that construct a lot of these objects per frame. After
changing the qHash implementation to be lighter we no longer rely on
qHashBits, so zeroing it is not essential anymore. Remove it.

Change-Id: If1fbd8dfd46fb3f0e9ea5a3c4794d24b8aeac1ba
Reviewed-by: Andy Nichols <andy.nichols@qt.io>