Feb 7 (Reuters) – A record 50.4 million American adults, or about 20% of the population, are expected to bet $16 billion on Sunday’s Super Bowl matchup between the Philadelphia Eagles and Kansas City Chiefs, the American Gaming Association said on Tuesday. The number of American adults planning to bet on the NFL’s title game is up 61% from a survey conducted last year by the trade group representing the U.S.casino industry, while the value of wagers is more than double last year’s estimates. With the expansion of legal sports betting the AGA said traditional bets made online, through a...