package/qt5imageformats: always use the opensource license

package/qt5imageformats: always use the opensource license

We never ask the user to confirm their assent about the use of a free
license; there is no reason we do so for Qt.

The output of legal-info is there to gather all the licenses used in a
build; the license for qt5imageformats will be there to be consulted as
well.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Julien Corjon <corjon.j@ecagroup.com>
Cc: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>