legacy/src/main/java/ucar/nc2/NetcdfFileWriteable.java
public Attribute deleteVariableAttribute(String varName, String attName) {
    if (!defineMode) throw new UnsupportedOperationException("not in define mode");
    Variable v = findVariable(varName);
    if (v == null) return null;

    Attribute att = v.findAttribute(attName);
    if (null == att) return null;

    v.remove(att);
    return att;
  }
public Attribute deleteVariableAttribute(String varName, String attName) {
    if (!defineMode) throw new UnsupportedOperationException("not in define mode");
    Variable v = findVariable(varName);
    if (v == null) return null;

    Attribute att = v.findAttribute(attName);
    if (null == att) return null;

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