Remove license text from the files that are not essential.

Remove the license text from files inside docs, examples and selftest,
to keep the license text only in relevant parts of the project.

References:

* https://fedoraproject.org/wiki/Packaging:LicensingGuidelines
* https://www.gnu.org/licenses/gpl-howto.html

Signed-off-by: Rudá Moura <rmoura@redhat.com>
Merge pull request #269 from ruda/remove_license_non_essential

Remove license text from the files that are not essential.