BOSTON — Massachusetts Taxpayers Foundation President Eileen McAnneny plans to step down from her post at the end of this year, she announced Wednesday. McAnneny in 2015 became the first woman to lead the business-backed organization. An influential player on Beacon Hill, MTF is closely watched by policymakers for its economic analysis, and is one of the groups that state budget-writers rely on for projections about future revenues and fiscal conditions.