Remove / fix obsolete docker-compose.yml: `version`

[jonkeane]

On main the test-connect CI is failing with:

b351d2874136 Pull complete 
 connect Pulled 
time="2025-03-04T21:46:23Z" level=warning msg="/home/runner/work/rsconnect-python/rsconnect-python/integration-testing/docker-compose.yml: `version` is obsolete"
 Network integration-testing_default  Creating
 Network integration-testing_default  Created

[tdstein]

These failures stem from this change in Connect: https://github.com/posit-dev/connect/commit/88ce4ff4d46ae1c4ba831e99b0136d86c0718cf3#diff-db146a204844f1dd26bd7bcafabfbd64d399001dd8bad4e7174611c628a8bfbe

It removed the Justfile commands that this CI uses (just test-rsconnect-python-repo).

The original intention was to ensure that changes to rsconnect-python would not break Connect's CI, which does the inverse operation. It pulls reconnect-python and uses it for its own test matrix. I think a better approach would be what we did with posit-sdk-py where we use Docker to run against the preview version of Connect. But, I think that's a larger lift.

All of this to say, now that rsconnect-python is in maintenance mode, I think it's reasonable to just remove the failing CI actions and rely on the tests in Connect to verify that it doesn't break its integration with rsconnect-python.

[tdstein]

Created #649 to track to the CI failure