LONDON (Reuters) - British Airways owner IAG scaled back its forecast for capacity growth for the next three years on Friday, hitting its outlook for earnings per share as the prospects for the global economy remained weak.IAG said available seat kilometres, a measure of passenger carrying capacity, was estimated to grow 3.4% a year between 2020 and 2022, compared to a previous forecast of 6% growth a year for the 2019-2023 period.The airline group, which also owns Iberia, Aer Lingus and..