In advance of a Sept. 25 vote by the Federal Communications Commission to ease telecommunication companies’ deployment of 5G wireless networks, the Marin County Board of Supervisors has sent a lengthy letter of opposition. The F.C.C. is seeking to ban state and local regulations designed to prohibit wireless infrastructure deployment and limit the fees cities can charge for reviewing 5G projects. Its order would also establish a 60-day shot-clock—a window of time from an application’s…