PR-K.3: chart cleanup (RBAC + values keys + NOTES.txt deprecation)

[trilamsr]

Per RFC-0013 §migration PR-K.3. PR-K.2 (#217) deleted in-tree receivers but deferred chart cleanup for one deprecation cycle. Scope:

• Delete install/kubernetes/tracecore/templates/containerstdout-rbac.yaml
• Remove {clockreceiver,kernelevents,k8sevents,containerstdout} values keys + JSON-schema entries from chart
• Add NOTES.txt deprecation warning for ~one minor version cycle before final removal
• Delete .github/ISSUE_TEMPLATE/component-bug-kernelevents.yml
• Verify helm template renders cleanly w/o deleted values

Operator-courtesy timing per RFC line 254.

[trilamsr]

PR #234 landed partial close — deleted 5 dead receiver/exporter toggles + containerstdout-rbac template + chart README + 3 ci fixtures (-390 LOC).

Out of scope of #234: k8sevents chart toggle (receiver itself still ships post-PR-B6 upstream port; toggle is live config, not dead).

Closing this issue. Remaining k8sevents cleanup will fold into PR-I.2 (#221) when receiver moves to module/.