remove unused static field, add comment

Author: timfel

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/CodecsModuleBuiltins.java

@@ -84,8 +84,6 @@
 
 @CoreFunctions(defineModule = "_codecs")
 public class CodecsModuleBuiltins extends PythonBuiltins {
-    public static final String DEFAULT_ENCODING = "utf-8";
-
     private static final Charset UTF32 = Charset.forName("utf-32");
 
     // python to java codecs mapping

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/str/StringBuiltins.java

@@ -1455,6 +1455,7 @@ private static int op(String self, String substr, int start) {
         }
     }
 
+    // This is only used during bootstrap and then replaced with Python code
     @Builtin(name = "encode", minNumOfPositionalArgs = 1, parameterNames = {"self", "encoding", "errors"})
     @GenerateNodeFactory
     @TypeSystemReference(PythonArithmeticTypes.class)