LOS ANGELES (Reuters) - The Republican presidential debate held without front-runner Donald Trump attracted 12.5 million viewers to Fox News Channel on Thursday, according to preliminary Nielsen data. Trump boycotted the event after Fox News, owned by 21st Century Fox, refused to yield to his demand that network anchor Megyn Kelly be replaced as a moderator.  (Reporting by Lisa Richwine; Editin gby Tom Brown) SAP is the sponsor of this coverage which is independently produced by the staff of Reuters News Agency.