[m-rev.] for review: delete references to Erlang in the compiler

[Peter Wang]

On Wed, 28 Oct 2020 03:04:23 +1100 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> The only nontrivial part of this is arranging short-term backwards compatibility
> in item_type_repn_infos, and since I am the expert on that, I thought I can do this
> more easily than Peter. Of course, this diff won't bootcheck until all Erlang foreign
> code is deleted from the system, which is a diff that Peter hasn't committed yet.
> Even after that, I intend to wait at least a day before committing this.

My own patch series was nearly ready as well, oh well. I didn't make the
change to item_type_repn_info so let's go with yours.

The major difference with my patch series is that I kept lang_erlang
around. The compiler would continue to accept pragma foreign_code,
foreign_type, etc. for a language "Erlang" but silently discard them.
The compiler would also continue to accept --libgrades-exclude erlang.
My plan was that we would leave these transition measures in place for
one or two major releases (six or 12 months).

I believe it wouldn't be difficult to add lang_erlang back into your
changes. Other than that, the changes are fine.

Peter