[Development] Removal of dead git submodules from qt5.git

[Alex Blasche]

Hi,

I would like to remove some of the ancient submodules from qt5.git. They never were part of the Qt 5 offering anyway and mostly we were not sure whether we reactivate them. Considering that we never had a use through Qt 5's life time, I think it's time to remove them from the default setup. Note that the git repo's stay around. You just have to manually add them to your checkout

In particular I am talking about:

 - qtdocgallery
 - qtfeedback
 - qtpim
 - qtsystems

If you disagree, please let me know and state a reason.

Thank you.

--
Alex