[m-rev.] for review: Delete references to Erlang backend in documentation.

[Julien Fischer]

On Mon, 26 Oct 2020, Peter Wang wrote:

> .INSTALL.in:
> .nocopyright:
> BUGS:
> README.Erlang:
> README.MS-VisualC:
> README.MacOS:
> README.MinGW:
> README.md:
> doc/reference_manual.texi:
> doc/user_guide.texi:
>    As above.
>
> NEWS:
>    Announce removal of Erlang backend.

That's fine.

Julien.