shell completions: add shell completion for docker rm --link and exclude legacy links for container names

[thaJeztah]

cli/command/completion: ContainerNames: skip legacy link names

Inline StripNamePrefix and skip legacy links for completion.
Legacy links can be removed from a container, but only when
using docker [container] rm --link <link-name>.

When linking containers through legacy links, a container can get multiple
names; its own name, and a name for each link it's providing:

# create two containers with links between them

docker run -d --name one nginx:alpine
docker run -d --name two --link one:link1 --link one:link2 --link one:link3 nginx:alpine

# container "one" now has multiple names
docker ps --no-trunc --format '{{.Names}}'
two
one,two/link1,two/link2,two/link3

# running `docker rm --link` with a link-name removes a link:

docker rm --link two/link3
docker ps --no-trunc --format '{{.Names}}'
two
one,two/link1,two/link2

# but without `--link`, it resolves the linked container and removes it:
docker rm -fv two/link2
two/link2
docker ps --no-trunc --format '{{.Names}}'
two

Legacy links are deprecated, and this can be confusing, so let's not provide
completion for secondary names.

cli/command/container: add shell completion for docker rm --link

When linking containers through legacy links, a container can get multiple
names; its own name, and a name for each link it's providing:

# create two containers with links between them
docker run -d --name one nginx:alpine
docker run -d --name two --link one:link1 --link one:link2 --link one:link3 nginx:alpine

docker rm --link <tab>
two/link1 two/link2 two/link3

- How to verify it

- Human readable description for the release notes

shell completions: add shell completion for `docker rm --link` and exclude legacy links for container names

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 66.66667% with 9 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cli/command/container/rm.go	12.50%	6 Missing and 1 partial ⚠️
cli/command/container/completion.go	86.66%	1 Missing and 1 partial ⚠️

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