Jimmy Fallon's guest lineup tonight just got nuked thanks to House Majority Leader Kevin McCarthy, who stunned Washington and TV news networks this morning by dropping his bid to succeed John Boehner as Speaker of the House. The vote to replace Boehner, aka third in line for the White House, has been postponed, and shocked cable news network on-air talent broke into regularly scheduled programming to announce. Just yesterday, NBC announced that the Tonight Show had…