Remove documentation sources from example injection packages

Documentation sources (/doc subdirectories and their contents)
for each example are removed from the installed examples
directory structure.

Task-number: QTBUG-33848
Change-Id: I1671e3d857e8966bb9e2d78de5c09563d180b438
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>