SINGAPORE, April 29 (Reuters) - China has waived the 125% tariff on ethane imports from the United States imposed earlier this month, two sources with knowledge of the matter said on Tuesday, among a group of products that have been granted exemptions. The move will ease pressure on Chinese firms that import U.S. ethane for petrochemical production as well as provide an outlet for the natural gas liquid, a byproduct of U.S. shale gas production. The sources said the tariff on ethane had been waived in recent days. One of them said the waiver has not been publicly announced. They...