Remove validation on uri field of app-control

Following the documentation, uri could
- point a ressource without defining a sheme
- be empty

so remove the uri check
BUG=XWALK-3223
Signed-off-by: Baptiste DURAND <baptiste.durand@open.eurogiciel.org>
Merge pull request #2750 from eurogiciel-oss/XWALK-3223

Remove validation on uri field of app-control