Remove useless check in AttachInterfacesTestJSON

In AttachInterfacesTestJSON, _check_interface won't do
anything if all optional params are not provided, so
this is to remove the useless _check_interface. Besides,
_test_show_interface already covers the check the author
might want to do.

Change-Id: I1a2382ed9f0c48c27017c973ba2a4831bf5a6119
1 file changed