Drop the dependence of Xy-pic from luatexja.dtx.

Drop the dependence of Xy-pic from luatexja.dtx.

But I couldn't typeset luatexja-ja.pdf with W32TeX (2012/5/25), with
the following error:

> [7]
>
> ! Package Listings Error: Couldn't load requested language.
>
> See the Listings package documentation for explanation.
> Type  H <return>  for immediate help.
>  ...
>
> l.456 \begin{LTXexample}
>
> ?