ci: remove obsolete Blockscout NPM publisher

[JOY (JOY)]

Summary

• remove the orphaned Blockscout toolkit NPM publisher workflow
• keep DOS release and Docker Hub publishing workflows unchanged

Evidence

• the workflow has zero standalone runs and no remaining internal or public callers
• the latest release attempt failed with npm error code ENEEDAUTH while trying to publish @blockscout/ui-toolkit@2.9.5-dos.1
• the repository does not define the required NPM_TOKEN secret
• npm registry metadata identifies blockscout/frontend as the package repository and lists upstream maintainers

Validation

• git diff --check
• no remaining NPM publisher workflow references
• actionlint adds no new findings; four unrelated pre-existing findings remain in checks.yml and stale-issues.yml