By Jude Summerfield Mikel Arteta has brought remarkable stability to Arsenal in recent years after a difficult start to life as manager, but the Spaniard has been dealt a large backroom blow with the exit of key club official Edu. The sporting director has helped the Gunners return to the top end of the Premier League table but news of his exit spread on Monday before it was confirmed by the north London giants that the Brazilian had resigned, the former midfielder himself describing it as an “an incredibly hard decision to make”. While he looks set to take a new role in a group of clubs owned…