cmake: remove useless SHARED from qi_create_python_ext() call

Change-Id: Ie8ad2c6bbc1bc7f57f8ba2ec4c67893d5eab66d8
Reviewed-on: http://gerrit.aldebaran.lan/50135
Reviewed-by: dmerejkowsky <dmerejkowsky@aldebaran-robotics.com>
Tested-by: dmerejkowsky <dmerejkowsky@aldebaran-robotics.com>