[gnu-soc] No GSOC this year for GNU

[Jose E. Marchesi]

After participating for 12 consecutive years, for the first time ever
the GNU Project got rejected as a mentoring organization in the Google
Summer of Code 2021.

We did not get any explanation other than: "We had many more
applications than available slots. We hope you will apply again in the
future!"

Thanks to the maintainers who prepared the ideas pages and did other
preparatory work.  Hopefully you will be able to use that material out
of the program.

Salud!