Remove unneeded function

The function TypeWithDict::hasDictionary() can be removed.   In ROOT6, it will not work correctly for enums, pointers, or C style arrays, because TypeWithDict does not necessarily have a correct type_info for these types.  The use of this function is replaced by use of the existing hasDictionary() free function, which takes the type_info as its input argument.
Please merge this as soon as convenient.