chore: remove static role assignment quota config

[roi (roivaz)]

Tracking: https://redhat.atlassian.net/browse/AROSLSRE-1789

What

• Remove roleAssignmentLimit from DEV CI source configuration and schema.
• Stop rendering the legacy field into Helm values and the exporter ConfigMap.

Why

The API-backed exporter introduced by #6494 no longer consumes a static role-assignment limit. Removing the field avoids stale duplicated quota data.

Rollout dependency: do not merge this PR until #6494 is merged, the tenant-quota-collector image is built, the image-updater has merged the new digest into config/config-dev-ci.yaml, and that image is deployed. The currently deployed binary defaults a missing limit to 4000, which would report incorrect limits for subscriptions configured at 8000.

Testing

• make -C config materialize
• make verify-schema
• make -C tooling/tenant-quota render-config
• confirmed rendered runtime config contains no roleAssignmentLimit

Special notes for your reviewer

Blocked on the code/image rollout from #6494. No reviewers have been requested or tagged; this draft is intentionally waiting for author review first.

Screenshots are not applicable because this only removes an obsolete configuration field and does not change metric names, labels, or visualizations.

PR Checklist

• PR is scoped to a single task (no mixed concerns)
• Title follows Conventional Commits format
• Summary explains the "Why" behind the change
• Linked to relevant ticket/issue
• Screenshots included (if graph/UI/metrics changes) — not applicable; no visualization change
• Self-reviewed the diff
• CI/CD checks are passing (ignore Tide) — pending draft PR CI
• Draft PR used for WIP (if applicable)
• Commit history is clean (rebased/squashed)
• Tricky code blocks are commented
• Specific reviewers tagged — intentionally deferred until author review
• All comment threads resolved before merge

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