By Jarrett Renshaw LANCASTER, PA. (Reuters) – Republicans in Pennsylvania chose on Saturday not to endorse a primary candidate in one of the most closely-watched U.S. Senate races in the country, amid concerns they could back a candidate in a crowded field who might put them at odds with Donald Trump. The endorsement of the state committee is widely considered the early prize of primary season, catapulting its recipient to the general election. This year, the party emerges from its winter meeting less unified ahead of a wide-open primary season. Trump has not said whether he will back any of t…