[debugger] remove step count parameter from prepare step.

test/mjsunit/harmony/debug-stepin-proxies.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --expose-debug-as debug --harmony-proxies
 
 Debug = debug.Debug
 
 var exception = null;
 var log = [];
 
 function listener(event, exec_state, event_data, data) {
   if (event != Debug.DebugEvent.Break) return;
   try {
     print(event_data.sourceLineText());
     var entry = "";
     for (var i = 0; i < exec_state.frameCount(); i++) {
       entry += exec_state.frame(i).sourceLineText().substr(-1);
       entry += exec_state.frame(i).sourceColumn();
     }
     log.push(entry);
-    exec_state.prepareStep(Debug.StepAction.StepIn, 1);
+    exec_state.prepareStep(Debug.StepAction.StepIn);
   } catch (e) {
     exception = e;
   }
 };
 
 var target = {};
 var handler = {
   has: function(target, name) {
     return true;                     // h
   },                                 // i
@@ skipping 36 matching lines @@
   "d0", "l4d11", "m2d11",                           // [[Set]]
   "e14", "r4e14", "q4r11e14", "s2e14",              // for-in [[Enumerate]]
       "o6e14", "q4e14", "p6e14", "q4e14", "q4e14",  // exhaust iterator
   "e9",                                             // for-in-body
       "h4e9","i2e9",                                // [[Has]] property
   "f2","foo", "e9",                                 // for-in-body
     "h4e9","i2e9",                                  // [[Has]]property
   "f2","bar", "e9",                                 // for-in-body
   "g0"
 ], log);