ci: remove manual publish.yml, rely on release-please.yml (#754)

## Summary
Removes the manual `Publish NPM` workflow. release-please.yml's embedded
publish job is the canonical path now that OIDC trust on npmjs.com is
set for `release-please.yml`.

## Why
- npm Trusted Publishers can target only one workflow file at a time per
package
- We picked `release-please.yml` so every release PR merge
auto-publishes with provenance
- `publish.yml` was the manual fallback we used to ship `smithery@1.0.0`
— no longer needed

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: calclavia