Remove legacy config path migration and fallbacks

[janHildebrandt98]

What?

Removed all code responsible for handling migration from the old legacy config file path to the new one.
Also dropped fallback logic.

Why?

The migration/fallback was intended to stick around for v1 only and, as a breaking change with v2, we are now intentionally removing it to simplify the code.

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 #5572

[janHildebrandt98]

@codebien
I am a little confused about the failed tests. After a brief investigation it seems like it is not touching the code i changed. Also on the other environments (as well as locally on my system) the tests seem to be green.

Is there something I am missing?

Edit:
After some more investigation this seems to happen because of some state/cache in json.Unmarshal() in go tip.
The race detector flags concurrent access to that cache because the tests are concurrently calling json.Unmarshal(). I don't think this is connected to this PR.

[codebien]

@janHildebrandt98 the fix is now merged, consider to rebase your pull request.

[janHildebrandt98]

@codebien
After a little Git adventure I noticed that rebasing is not a good idea since we want to merge into v2 and there are a bunch of differences to master, were you merged the fix.
I just removed my equivalent change so we only have the removal of the migration stuff in here now. I guess there will be a sync between v2 and master at some point?
Git history of this PR is kind of a mess now :D

[janHildebrandt98]

@codebien
Do I need to do something here or can we proceed?

[codebien]

Hey thanks for you contribution!

[codebien]

We want to keep the testing for the current path. We should only drop the ones related to the legacy.

[janHildebrandt98]

TestLoadConfig() tested the loadConfig() method which I removed because it was just a wrapper around readDiskConfig() to decide from where to load the config (legacy vs. new).
Thats why I think the whole test is obsolete now. The logic is sufficiently tested by the tests for readDiskConfig() which is now called everywhere directly.

[codebien]

After a little Git adventure I noticed that rebasing is not a good idea since we want to merge into v2 and there are a bunch of differences to master, were you merged the fix.

Yep, we are aware of it. I'm going to rebase v2, as soon as possible.

[codebien]

v2 is now in sync with master, you can rebase your branch

[janHildebrandt98]

@codebien
I rebased on v2 and answered your comment.
Thanks you for your time to review the PR.