By Elizabeth Piper and Kate Holton LONDON (Reuters) -Britain published plans on Monday to override some post-Brexit trade rules for Northern Ireland by scrapping checks and challenging the role played by the European Union’s court in a new clash with Brussels. Despite Ireland describing the move as a “new low” and Brussels talking of damaged trust, Britain pressed ahead with what Prime Minister Boris Johnson suggested were “relatively trivial” steps to improve trade and reduce bureaucracy. European Commission Vice President Maros Sefcovic said Brussels’ reaction would be proportionate, but rul…