legacy/src/main/java/ucar/nc2/NetcdfFileWriteable.java
public Attribute deleteGlobalAttribute(String attName) {
    if (!defineMode) throw new UnsupportedOperationException("not in define mode");
    Attribute att = findGlobalAttribute(attName);
    if (null == att) return null;

    rootGroup.remove(att);
    return att;
  }
public Attribute deleteGlobalAttribute(String attName) {
    if (!defineMode) throw new UnsupportedOperationException("not in define mode");
    Attribute att = findGlobalAttribute(attName);
    if (null == att) return null;

    rootGroup.remove(att);
    return att;
  }
Delete a global Attribute. Must be in define mode.
@param attName existing Attribute has this name
@return deleted Attribute, or null if not found