Drop `labels: ["triage"]` from issue templates

[Yicong-Huang]

Task Summary

After PR #4899 retired the triage label workflow, new issues opened from the bug / task / feature templates still attach triage because each template carries labels: ["triage"]. Drop the line in all three templates so newly opened issues match the simplified is:issue is:open no:assignee filter directly.

Task Type

• Code Implementation