[debugger] remove step count parameter from prepare step.

test/mjsunit/es6/debug-promises/stepin-handler.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 --allow-natives-syntax --noalways-opt
 // Tests stepping into through Promises.
 
 Debug = debug.Debug
 var exception = null;
 var break_count = 0;
 var expected_breaks = -1;
 
 function listener(event, exec_state, event_data, data) {
   try {
     if (event == Debug.DebugEvent.Break) {
       assertTrue(exec_state.frameCount() != 0, "FAIL: Empty stack trace");
       if (!break_count) {
         // Count number of expected breakpoints in this source file.
         var source_text = exec_state.frame(0).func().script().source();
         expected_breaks = source_text.match(/\/\/\s*Break\s+\d+\./g).length;
         print("Expected breaks: " + expected_breaks);
       }
       var source = exec_state.frame(0).sourceLineText();
       print("paused at: " + source);
       assertTrue(source.indexOf("// Break " + break_count + ".") > 0,
                  "Unexpected pause at: " + source + "\n" +
                  "Expected: // Break " + break_count + ".");
       ++break_count;
       if (break_count !== expected_breaks) {
-        exec_state.prepareStep(Debug.StepAction.StepIn, 1);
+        exec_state.prepareStep(Debug.StepAction.StepIn);
       }
     }
   } catch(e) {
     exception = e;
     print(e, e.stack);
   }
 };
 
 Debug.setListener(listener);
 
@@ skipping 15 matching lines @@
 function callback(x) {
   return x; // Break 2. // Break 4. // Break 6.
 } // Break 3. // Break 5. // Break 7.
 
 function finalize() {
   assertNull(exception); // Break 8.
   assertEquals(expected_breaks, break_count);
 
   Debug.setListener(null);
 }