Tracking issue for post-libnetwork integration tasks after #42262:

• update BuildKit to use the new import paths, and upstream changes from: moby/buildkit@244e8cd...cpuguy83:update_libnetwork_import (PR: Update docker/docker to master / v21.xx-dev (post libnetwork integration) buildkit#2150)
  • re-vendor BuildKit to remove the temporary fork (PR: revendor BuildKit (master branch) #42473)
• update SwarmKit to use the new import paths moby/swarmkit@5a5494a...cpuguy83:switch_libnetwork (PR1: update to github.com/docker/docker v20.10.7 (and dependencies), Go 1.13.15 swarmkit#3004, PR2: update to docker/docker v21.xx-dev (master), and remove libnetwork swarmkit#3005)
  • re-vendor SwarmKit to remove the temporary fork (PR: vendor: swarmkit master (after libnetwork move) #42474)
• look into test-failures / flakiness after integration
• Address review comments from Move libnetwork #42262
  • remove left-over files (circleci config, maintainers file, etc) (some done in libnetwork: remove some things that are no longer needed #42498)
  • replace github.com/urfave/cli with spf13/cobra
  • replace mflags package with spf13/pflags
  • get rid of some of the //nolint:gosec comments (where possible)
• Review/migrate/close open pull requests in libnetwork
  • Write instructions on how to migrate pull requests from libnetwork to moby
  • Leave comments on existing PRs with instructions
  • Close pull requests that are no longer relevant
• Update docker/libnetwork repository description and readme to describe status (deprecated, moved)
• Archive the docker/libnetwork repository once we no longer need it
• TBD: discuss if we want to backport Move libnetwork #42262 to the 20.10 branch, so that we don't have to maintain libnetwork changes in two locations