Nearly 300,000 people remained without power last night in the wake of the second nor’easter to hit Massachusetts in a week, and many of those outages are expected to last into the weekend, utility spokespeople said.As of 7:15 p.m., more than 277,924 households and businesses had no electricity, mostly in Eastern Massachusetts, according to the Massachusetts Emergency Management Agency. The bulk of them — 223,230 — were National Grid customers, largely in the Merrimack Valley, MEMA said.