MOUND BAYOU, Miss. — In the center of this historically Black city, once deemed “the jewel of the Delta” by President Theodore Roosevelt, dreams to revitalize an abandoned hospital building have all but dried up. An art deco sign still marks the main entrance, but the front doors are locked, and the parking lot is empty. These days, a convenience store across North Edwards Avenue is far busier than the old Taborian Hospital, which first shut down more than 40 years ago. Myrna Smith-Thompson, who serves as executive director of the civic group that owns the property, lives 100 miles away in Mem…