Morgan Stanley, Wall Street’s biggest stock-trading firm by revenue, is cutting its global bonus pool for the equities division by as much as 4 percent and dismissing some employees after the industry’s results flagged last year, according to people with knowledge of the plans. The firm, which is set to pay annual bonuses next month, has been fine-tuning calculations for pay packages since November, according to the people, who asked not to be identified describing the deliberations.