ci: drop run-docker scripts

ci: drop run-docker scripts

We haven't used these scripts since 4a6e4b9602 (CI: remove Travis CI
support, 2021-11-23), as the GitHub Actions config has support for
directly running jobs within docker containers.

It's possible we might want to resurrect something like this in order to
be more agnostic to the CI platform. But it's not clear exactly what it
would look like. And in the meantime, it's just a maintenance burden as
we make changes to CI config, and is subject to bitrot. In fact it's
already broken; it references ci/install-docker-dependencies.sh, which
went away in 9cdeb34b96 (ci: merge scripts which install dependencies,
2024-04-12).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>