chore: drop attribution rules that duplicate the global instructions

The commit-trailer and PR-footer rules in this repo's release skill duplicated the
global agent instructions, and the copy had drifted: it named a trailer identity
the global rule explicitly rules out.

Removed rather than corrected. A local copy of a global rule cannot stay correct,
and once stale it competes with its source instead of reinforcing it. Attribution
is now defined in exactly one place.

Co-Authored-By: plan-marshall <noreply@cuioss.de>

Author: cuioss-oliver

.claude/skills/release/SKILL.md

@@ -120,8 +120,6 @@ gh pr create --repo cuioss/cui-test-value-objects --base main \
   --body "Bump current-version to <version>. Triggers the automated Release workflow on merge."
 ```
 
-Commit trailer: `Co-Authored-By: Claude <noreply@anthropic.com>` — no model name, no
-"Generated with Claude Code" footer.
 
 ### Step 7 — Wait for PR checks