BARCELONA, Spain—Impromptu street celebrations erupted across Spain as the clock struck midnight on Saturday, when a six-month-long national state of emergency to contain the spread of coronavirus ended and many nighttime curfews were lifted. In Madrid, police had to usher revelers out of the central Puerta del Sol square, where the scenes of unmasked dancing and group singing mimicked pre-pandemic nightlife. Teenagers and young adults also poured into central squares and beaches of Barcelona to mark the relaxation of restrictions. “Freedom!” said Juan Cadavid, who was reconnecting with friends. “(It’s) a bit scary, you know, because of COVID, but I want to feel like this around a lot of people.” The 25-year-old Barcelona resident was also rejoicing at the prospect of going back to work at a Michelin-star restaurant that has been closed for the past seven months due to pandemic-related restrictions. Local restaurants will be able to serve dinner …