Remove now unused 'preserve_entities' option on escapeXml.

This was formerly used (incorrectly) in the HTML renderer.
It isn't needed any more.

[API change]

lib/common.js

@@ -37,8 +37,6 @@ var XMLSPECIAL = '[&<>"]';
 
 var reXmlSpecial = new RegExp(XMLSPECIAL, 'g');
 
-var reXmlSpecialOrEntity = new RegExp(ENTITY + '|' + XMLSPECIAL, 'gi');
-
 var unescapeChar = function(s) {
     if (s.charCodeAt(0) === C_BACKSLASH) {
         return s.charAt(1);
@@ -80,13 +78,9 @@ var replaceUnsafeChar = function(s) {
     }
 };
 
-var escapeXml = function(s, preserve_entities) {
+var escapeXml = function(s) {
     if (reXmlSpecial.test(s)) {
-        if (preserve_entities) {
-            return s.replace(reXmlSpecialOrEntity, replaceUnsafeChar);
-        } else {
-            return s.replace(reXmlSpecial, replaceUnsafeChar);
-        }
+        return s.replace(reXmlSpecial, replaceUnsafeChar);
     } else {
         return s;
     }