readline: don't use Function#call()

It wasn't necessary.

lib/readline.js

@@ -350,13 +350,13 @@ Interface.prototype._tabComplete = function() {
         for (var i = 0, compLen = completions.length; i < compLen; i++) {
           c = completions[i];
           if (c === '') {
-            handleGroup.call(self, group, width, maxColumns);
+            handleGroup(self, group, width, maxColumns);
             group = [];
           } else {
             group.push(c);
           }
         }
-        handleGroup.call(self, group, width, maxColumns);
+        handleGroup(self, group, width, maxColumns);
 
         // If there is a common prefix to all matches, then apply that
         // portion.
@@ -373,8 +373,7 @@ Interface.prototype._tabComplete = function() {
 };
 
 // this = Interface instance
-function handleGroup(group, width, maxColumns) {
-  var self = this;
+function handleGroup(self, group, width, maxColumns) {
   if (group.length == 0) {
     return;
   }