fix: track upstream renames in SimpLC

`exceptBoolEmoji` was removed when `TraceResult` replaced `ExceptToEmoji`
(#12698); `withTraceNode` now prefixes the emoji itself, so the header
message just drops it. `DiscrTree.values` moved to `Lean.Meta.DiscrTree.Util`
in the `DiscrTree` refactor (#11875), which `Lean.Meta.Tactic.Simp.SimpTheorems`
no longer pulls in, so import it directly.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WGQ4cXuC9bBbZQ3psYLZUA