ci: remove obsolete Kubernetes E2E workflow

[JOY (JOY)]

Summary

• remove the unused Kubernetes E2E workflow inherited from Blockscout
• eliminate a manual and reusable entrypoint with broad write permissions and inherited secrets
• keep the active Playwright CI, Docker publisher, and shared deployment templates unchanged

Evidence

• workflow ID 71308910 has zero recorded runs
• the repository has zero GitHub deployments and zero GitHub environments
• no repository in the DOS organization references this reusable workflow
• the workflow targets vault.k8s.blockscout.com, blockscout/deployment-values, and blockscout-ci-cd
• repository variables and secrets are DOS Docker Hub credentials, not Blockscout Vault credentials

Validation

• git diff --check origin/main...HEAD
• no remaining e2e-tests.yml, Run E2E tests k8s, blockscout-ci-cd, or deployment-values references under repository automation paths
• full actionlint reports only pre-existing findings in checks.yml, publish-image.yml, and stale-issues.yml