less stats in the exam

[WandrilleD]

As we scale down the stat part of the course, we should also scale it down in the exam.
I can be replaced by more plotting for example

[dianamarek]

Apart from changing a sentence regarding the test of normality, i did not remove anything else for the June course but of course will adapt to what will be covered in the end. I let you decide wether you want to keep this issue open or closed.