Fix regression in JSON serialization of RegExps.

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index c7835660d339e79a2dc2a3528fc29ca5ca249ffe..c19f4a9a683a40b6c8cdefae14893008419c8481 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -190,7 +190,6 @@ function FormatMessage(message) {
       illegal_return:               "Illegal return statement",
       error_loading_debugger:       "Error loading debugger",
       no_input_to_regexp:           "No input to %0",
-      result_not_primitive:         "Result of %0 must be a primitive, was %1",
       invalid_json:                 "String '%0' is not valid JSON",
       circular_structure:           "Converting circular structure to JSON",
       obj_ctor_property_non_object: "Object.%0 called on non-object",