PHILADELPHIA — Montgomery County Commissioner Val Arkoosh, a physician and the lone woman in the top tier of Pennsylvania’s Democratic Senate primary candidates, is dropping out of the race. “It’s become increasingly clear over the last month or two that I’m unlikely to be the Democratic nominee,” Arkoosh said in an interview Friday ahead of an announcement. “And in my book there’s just nothing more important than flipping this seat and I think the thing I can do to best ensure that is to suspend my campaign.” She said she doesn’t plan to endorse in the primary but will campaign for the Democr…