ARROW-15866: [Packaging][Ubuntu] Drop support for Ubuntu 21.04

[kou]

It reached EOL at 2022-01.

[kou]

@github-actions crossbow submit ubuntu-*

[github-actions]

Revision: 2e501bf

Submitted crossbow builds: ursacomputing/crossbow @ actions-1726

Task	Status
ubuntu-bionic-amd64
ubuntu-bionic-arm64
ubuntu-focal-amd64
ubuntu-focal-arm64
ubuntu-impish-amd64
ubuntu-impish-arm64

[pitrou]

There are also some references to 21.04 in dev/tasks/tasks.yml, should be bump them to 21.10?
Also, there's ci/docker/ubuntu-21.04-cpp.dockerfile.

[kou]

I don't want to mix the task to this pull request.
I've created an issue for it: ARROW-15873

[kou]

+1

[github-actions]

https://issues.apache.org/jira/browse/ARROW-15866

[github-actions]

⚠️ Ticket has not been started in JIRA, please click 'Start Progress'.

[ursabot]

Benchmark runs are scheduled for baseline = 2fea818 and contender = 8f901e0. 8f901e0 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished ⬇️0.0% ⬆️0.0%] ec2-t3-xlarge-us-east-2
[Finished ⬇️0.25% ⬆️0.0%] test-mac-arm
[Finished ⬇️0.0% ⬆️0.0%] ursa-i9-9960x
[Finished ⬇️0.0% ⬆️0.0%] ursa-thinkcentre-m75q
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java