Remove unreachable utility functions (bd-224, bd-214)

- Remove duplicate computeIssueContentHash from sqlite/hash.go
- Remove FileUsed() from internal/config/config.go
- Remove verifyIssueOpen() test helper from git_sync_test.go
- Remove unimplemented SummarizeTier2 and all tier2 infrastructure from haiku.go

Removes ~120 LOC of dead code identified by deadcode analyzer.

Amp-Thread-ID: https://ampcode.com/threads/T-5f150c35-8d67-4dae-bb92-a7b5887d649d
Co-authored-by: Amp <amp@ampcode.com>

internal/storage/sqlite/hash.go

@@ -2,41 +2,10 @@ package sqlite
 
 import (
 	"context"
-	"crypto/sha256"
 	"database/sql"
-	"encoding/hex"
-	"encoding/json"
 	"fmt"
-	"time"
-
-	"github.com/steveyegge/beads/internal/types"
 )
 
-// computeIssueContentHash computes a SHA256 hash of an issue's content, excluding timestamps.
-// This is used for detecting timestamp-only changes during export deduplication.
-func computeIssueContentHash(issue *types.Issue) (string, error) {
-	// Clone issue and zero out timestamps to exclude them from hash
-	normalized := *issue
-	normalized.CreatedAt = time.Time{}
-	normalized.UpdatedAt = time.Time{}
-	
-	// Also zero out ClosedAt if present
-	if normalized.ClosedAt != nil {
-		zeroTime := time.Time{}
-		normalized.ClosedAt = &zeroTime
-	}
-	
-	// Serialize to JSON
-	data, err := json.Marshal(normalized)
-	if err != nil {
-		return "", err
-	}
-	
-	// SHA256 hash
-	hash := sha256.Sum256(data)
-	return hex.EncodeToString(hash[:]), nil
-}
-
 // GetExportHash retrieves the content hash of the last export for an issue.
 // Returns empty string if no hash is stored (first export).
 func (s *SQLiteStorage) GetExportHash(ctx context.Context, issueID string) (string, error) {