Slideshow ( 2 images ) LONDON (Reuters) -A U.S. regulator has dropped a case against two former top London currency traders that alleged exchange-rate rigging, the agency said on Thursday, drawing a line under an eight-year pursuit by U.S. authorities. The U.S. Office of Comptroller of the Currency (OCC) withdrew its case in federal court against Richard Usher, an ex JPMorgan head of EMEA foreign exchange spot trading, and Rohan Ramchandani, Citigroup’s former European forex trading head, according to their lawyers, the agency and a court notice. “The agency made its decision to drop the ...