Some of America’s biggest shale producers are beginning to ratchet back oil and gas production for the first time in years, bending to the reality that a global glut will keep prices depressed. The production cuts, announced as shale companies reported dismal earnings in recent days, stand in stark contrast to the past year, when many U.S. drillers kept the taps turned on even as oil prices plunged from nearly $100 a barrel to about…