executor: remove containerd

[sluongng]

We no longer use containerd or ctr in any of the isolation options.
Remove the vendored binaries as well as the debian package installation
in the executor container image.

[iain-macdonald]

Per https://buildbuddy-corp.slack.com/archives/C01D5GHRJ59/p1760704931417589 LMK when you've confirmed docker still works in this context.

[sluongng]

I finally had some time to test this today.

sluongng/rm-containerd ~/work/buildbuddy-io/buildbuddy> bazel run enterprise/server/cmd/executor:executor_image

INFO: Invocation ID: 0a155663-0546-40a6-b8c3-a24425fca3b0
INFO: Analyzed target //enterprise/server/cmd/executor:executor_image (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
Target //enterprise/server/cmd/executor:executor_image up-to-date:
  bazel-bin/enterprise/server/cmd/executor/executor_image-layer.tar
INFO: Elapsed time: 0.766s, Critical Path: 0.04s
INFO: 1 process: 14 action cache hit, 1 internal.
INFO: Build completed successfully, 1 total action
INFO: Running command line: bazel-bin/enterprise/server/cmd/executor/executor_image.executable
Loading legacy tarball base _main/../+_repo_rules2+executor_image/image/dockerfile_image.tar...
Loaded image: executor_image:dockerfile_image
e0b5a67fc674: Loading layer [==================================================>]  30.72kB/30.72kB
6ac3d1a5f522: Loading layer [==================================================>]  7.537MB/7.537MB
5e9543f4c7e0: Loading layer [==================================================>]  10.24kB/10.24kB
b17f14ca4d75: Loading layer [==================================================>]  11.87MB/11.87MB
89b919f95b17: Loading layer [==================================================>]  14.18MB/14.18MB
766186e6b26e: Loading layer [==================================================>]  7.373MB/7.373MB
56a41dc8badd: Loading layer [==================================================>]  76.05MB/76.05MB
7cda0a84a524: Loading layer [==================================================>]  10.24kB/10.24kB
12a0223b58ad: Loading layer [==================================================>]  344.1MB/344.1MB
84ff92691f90: Loading layer [==================================================>]  10.24kB/10.24kB
Loaded image ID: sha256:bf5cd271f4a13c621e37d65d860a7fb86d58fffa9efb0131a15fb4cc3c3f6398
Tagging bf5cd271f4a13c621e37d65d860a7fb86d58fffa9efb0131a15fb4cc3c3f6398 as bazel/enterprise/server/cmd/executor:executor_image
sluongng/rm-containerd ~/work/buildbuddy-io/buildbuddy> docker run --rm -it --entrypoint="" bazel/enterprise/server/cmd/executor:executor_image bash
root@87af266fcb0a:/app/enterprise/server/cmd/executor/executor.runfiles/_main# which docker
/usr/bin/docker
root@87af266fcb0a:/app/enterprise/server/cmd/executor/executor.runfiles/_main# which ctr
/usr/bin/ctr
root@87af266fcb0a:/app/enterprise/server/cmd/executor/executor.runfiles/_main# ctr --version
ctr containerd.io v1.7.28
root@87af266fcb0a:/app/enterprise/server/cmd/executor/executor.runfiles/_main# containerd --version
containerd containerd.io v1.7.28 b98a3aace656320842a23f4a392a33f46af97866
root@87af266fcb0a:/app/enterprise/server/cmd/executor/executor.runfiles/_main# docker ps
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
root@87af266fcb0a:/app/enterprise/server/cmd/executor/executor.runfiles/_main#

So with the pinned version removed, ctr and containerd got pulled in transitively from the Docker Debian package and got a minor version bump.