refactor(gmail): remove dead code in primarySendAsDisplayNameFromList

The condition `primary == nil && sa.IsPrimary` inside the email-matching
block can never be true because `primary` is already unconditionally set
to `sa` when `sa.IsPrimary` is true earlier in the same loop iteration.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: salmonumbrella

internal/cmd/gmail_send.go

@@ -285,9 +285,6 @@ func primarySendAsDisplayNameFromList(ctx context.Context, svc *gmail.Service, a
 			if displayName := strings.TrimSpace(sa.DisplayName); displayName != "" {
 				return displayName, nil
 			}
-			if primary == nil && sa.IsPrimary {
-				primary = sa
-			}
 		}
 	}