Remove stale telemetry leftovers

[mnapoli]

Telemetry was removed a while ago, but a few leftovers survived. This cleans them up:

• Deleted lib/utils/get-framework-id.js, lib/utils/npm-package/is-global.js and lib/utils/telemetry/are-disabled.js: all unused.
• Deleted the disable-serverless-stats-requests test helper, which existed only to stub the module above.
• Removed the variableSourcesInConfig tracking in the variables resolver: it recorded variable sources for telemetry, nothing reads it anymore.
• Rewrote the outdated comments that still referenced the old generatePayload telemetry logic.

The accountId prefetch in deploy/remove and provider.accountId are kept as-is (plugins may rely on them), only their comments changed.

Bref is not affected: it reads frameworkId through the @serverless/utils/config alias, which points to the vendored config.js. Both are untouched, and I verified Bref's exact code path (from current bref master) still works against this branch.

[GrahamCampbell]

We need to be careful removing some of these, as they may be used by people requiring the package (Bref was using some stuff adjacent to this for example).

[mnapoli]

Yep, I'm fine dropping this if it's too risky. I've asked Fable to minimize risky deletes, that's why I ended up leaving one of the variable. I think what's left should be fine to merge, but this PR is not a priority tbh.