Simplify line editor choice in d8.

src/d8.h

Index: src/d8.h
diff --git a/src/d8.h b/src/d8.h
index 1c3ce0a122ec8bbe776f42332001ef81b77cdf3c..f3b3fa1728e95c8aa6e7ac5c820197bf603b8a66 100644
--- a/src/d8.h
+++ b/src/d8.h
@@ -128,12 +128,11 @@ class LineEditor {
   virtual void AddHistory(const char* str) { }
 
   const char* name() { return name_; }
-  static LineEditor* Get();
+  static LineEditor* Get() { return current_; }
  private:
   Type type_;
   const char* name_;
-  LineEditor* next_;
-  static LineEditor* first_;
+  static LineEditor* current_;
 };