THE “angel of the accordion” died Sunday and a familiar, cheerful figure has left the Ann Arbor scene. We refer, of course, to Mrs. George Muehlig who for years played her accordion and and gave of her time in hospitals for the aged, for veterans, for children, for the mentally retarded and the physically handicapped. “I can’t claim I do it for other people,” she once remarked. “I do it for myself. It’s what I want to do.” Then, typically, she would sling her 10-pound accordion over her shoulder and be off to bring her special brand of cheer to another institution. Ann Arbor will miss Mrs. Muehlig.