[cmake-developers] Make sure we always find the FindQt4.cmake shipped with CMake itself

[Stephen Kelly]

Brad King wrote:
> Currently these topics are open on the stage relating to Qt4/5:
> 
> * workaround-usr-move-qt5: I think this can be reverted.
>   It never fixed the problem on Marcus' machine fully and
>   I think he upgraded Qt to make the problem go away.

I thought the same. Done.

> * fix-build-without-qt4-with-qt5: Introduces this problem

Reverted that patch.

Thanks,

Steve.