the sort option is broken anyway, removed it

we need to mangle names from outermost to innermost scope; mangling names
from inner scopes before we got to the outer scope won't work correctly,
therefore sorting doesn't make sense.

lib/scope.js

@@ -329,7 +329,6 @@ AST_Symbol.DEFMETHOD("global", function(){
 
 AST_Toplevel.DEFMETHOD("mangle_names", function(options){
     options = defaults(options, {
-        sort   : false,
         except : []
     });
     // We only need to mangle declaration nodes.  Special logic wired
@@ -368,11 +367,6 @@ AST_Toplevel.DEFMETHOD("mangle_names", function(options){
         }
     });
     this.walk(tw);
-
-    if (options.sort) to_mangle = mergeSort(to_mangle, function(a, b){
-        return b.references.length - a.references.length;
-    });
-
     to_mangle.forEach(function(def){ def.mangle(options) });
 });