[devtools/test] drop legacy cube i18n tests test_i18ncube_legacy_layout() is droped and make others tests uses a new style cube "cubicweb_i18ntestcube", so it doesn't depends on legacy cube machinery.

Upstream Author:

  %(author)s <%(author-email)s>

Copyright:

Copyright (c) %(year)s %(author)s.
%(author-web-site)s -- mailto:%(author-email)s