V2 Update leaves old versions behind

Confirm by changing [ ] to [x] below to ensure that it's a bug:
- [x] I've gone though the [User Guide](https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-welcome.html) and the [API reference](https://docs.aws.amazon.com/cli/latest/reference/)
- [x] I've searched for [previous similar issues](https://github.com/aws/aws-cli/issues) and didn't find any solution

**Describe the bug**
When I update the aws-cli v2 on linux, using the instructions [here](https://docs.aws.amazon.com/cli/latest/userguide/install-cliv2-linux.html#cliv2-linux-upgrade), it doesn't remove old versions of the awscli. So after several updates I end up with gigabytes of space used by old versions of aws-cli.

**Platform/OS/Hardware/Device**
Linux

**To Reproduce (observed behavior)**
Follow instructions at https://docs.aws.amazon.com/cli/latest/userguide/install-cliv2-linux.html#cliv2-linux-upgrade to upgrade aws-cli to a new version. Then inspect the folder where the aws-cli is installed, and see old versions still there.

**Expected behavior**
Upgrading aws-cli shouldn't leave behind old versions.

Or better yet, provide ways to install aws-cli v2 using actual package managers like apt, dnf, maybe PyPi (see #4947) that handles cleaning up old files on upgrade.