remove enable community extensions flag

[pablochacin]

What?

Removes the enable community extensions flag and the need to adjust the build service's URL to select the oss catalog when they were enabled.

Why?

After alll extensions were integrated into a single catalog that includes both official and community extensions, and all these extensions are supported in GCK6, there's no need to explicitly enable community extensions.

Checklist

• I have performed a self-review of my code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have added tests for my changes.
• I have run linter and tests locally (make check) and all pass.

Checklist: Documentation (only for k6 maintainers and if relevant)

Please do not merge this PR until the following items are filled out.

• I have added the correct milestone and labels to the PR.
• I have updated the release notes: link
• I have updated or added an issue to the k6-documentation: grafana/k6-docs#NUMBER if applicable
• I have updated or added an issue to the TypeScript definitions: grafana/k6-DefinitelyTyped#NUMBER if applicable

Related PR(s)/Issue(s)

Closes https://github.com/grafana/k6-cloud/issues/3747

[codebien]

@pablochacin Is it really a breaking change? In the end the behavior is not changing. If this is really a breaking change then we have to work-around it because it isn't allowed in v1.x, or we have to wait for v2.x.

[pablochacin]

@codebien I think it is a breaking change in the sense that users can't opt out of community extensions.
Also, we are removing an environment variable and in my understanding those are part of the API

[codebien]

@pablochacin I now agree with you, this is a breaking change and it isn't allowed so we have to discuss how to make it backward compatible, or wait for v2.