Remove set-issue-field safe output (not yet supported by compiler)

Keep field-related instructions in the prompt body so the agent
can still recommend field values in the triage report.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: labudis

workflows/issue-triage.md

@@ -25,8 +25,6 @@ safe-outputs:
   add-comment:
   set-issue-type:
     max: 1
-  set-issue-field:
-    max: 5
 
 tools:
   web-fetch: