fix: trigger Maven deploy on release-please published events (#1966)

## Summary

- Add `release: published` trigger to the deploy workflow so it fires
when release-please creates a GitHub Release (the existing `push: tags`
trigger doesn't fire because release-please uses `GITHUB_TOKEN` via the
API)
- Remove unused `.github/release.yml` (release notes config that was
never
  applied — release-please supplies its own changelog)

## Test plan

- [x] Manually re-triggered v1.6.0 deploy by re-pushing the tag
- [ ] Next release-please release should automatically trigger the
deploy

Signed-off-by: Gregor Zeitlinger <gregor.zeitlinger@grafana.com>

Author: zeitlinger

.github/release.yml

@@ -5,6 +5,9 @@ on:
   push:
     tags:
       - "v*.*.*"
+  release:
+    types:
+      - published
 
 jobs:
   deploy: