DUBLIN (Reuters) – Allied Irish Banks will pay NatWest Group 5.4 billion euros ($5.75 billion) to acquire its Irish tracker mortgage book as the British lender moves towards completing its exit from Ireland. NatWest announced 15 months ago that it was winding down its Irish Ulster Bank unit and said on Wednesday that it had binding agreements in place for 90% of a total loan book that stood at about 20 billion euros. AIB said the loans were worth 5.7 billion euros and would add 47,000 customers to the bank. The mortgages, which track the European Central Bank interest rate, a product no longer…