CODE_OF_CONDUCT.md: update PLC members list

CODE_OF_CONDUCT.md: update PLC members list

As part of our code of conduct, we maintain a list of active members on
the Project Leadership Committee, which serves a couple of purposes. The
details are in 3f9ef874a7 (CODE_OF_CONDUCT: mention individual
project-leader emails, 2019-09-26), but the gist is as follows:

  - It makes it clear that people with a CoC complaint may contact
    members individually as opposed to the general PLC list (in case the
    subject of their complaint has to do with one of the committee
    members).

  - It also serves as the de-facto list of people on the PLC, which
    isn't committed anywhere else in the tree.

As of [1], Peff is no longer a member of Git's Project Leadership
Committee. Let's update the list of active members accordingly [2].

This also gives us a convenient opportunity to thank Peff for his many
years of service on the PLC, during which he helped the Git community in
more ways than we can easily list here.

[1]: https://lore.kernel.org/git/YboaAe4LWySOoAe7@coredump.intra.peff.net/
[2]: https://lore.kernel.org/git/CAP8UFD2XxP9r3PJ4GQjxUbV=E1ASDq1NDgB-h+S=v-bZQ7DYwQ@mail.gmail.com/

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>