[debugger] remove step count parameter from prepare step.

test/mjsunit/regress/regress-147497.js

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 13 matching lines @@
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 // Flags: --expose-debug-as debug
 
 Debug = debug.Debug;
 
 function listener(event, exec_state, event_data, data) {
   if (event == Debug.DebugEvent.Break) {
-    exec_state.prepareStep(Debug.StepAction.StepNext, 10);
+    exec_state.prepareStep(Debug.StepAction.StepNext);
   }
 };
 
 Debug.setListener(listener);
 
 var statement = "";
 for (var i = 0; i < 1024; i++) statement += "z";
 statement = 'with(0)' + statement + '=function foo(){}';
 
 debugger;
 eval(statement);