[debugger] remove step count parameter from prepare step.

test/mjsunit/debug-return-value.js

 // Copyright 2010 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 80 matching lines @@
               assertEquals(debugger_source_position + 19,
                            exec_state.frame(0).sourcePosition());
             } else {
               assertEquals(debugger_source_position + 38,
                            exec_state.frame(0).sourcePosition());
             }
             break;
           default:
             fail("Unexpected");
         }
-        exec_state.prepareStep(Debug.StepAction.StepIn, 1);
+        exec_state.prepareStep(Debug.StepAction.StepIn);
       } else {
         // Position at the end of the function.
         assertEquals(debugger_source_position + 50,
         exec_state.frame(0).sourcePosition());
 
         // Just about to return from the function.
         assertTrue(exec_state.frame(0).isAtReturn())
         assertEquals(expected_return_value,
                      exec_state.frame(0).returnValue().value());
 
@@ skipping 43 matching lines @@
 assertTrue(listener_complete);
 assertEquals(4, break_count);
 
 break_count = 0;
 expected_return_value = 2;
 listener_complete = false;
 f(false);
 assertFalse(exception, "exception in listener")
 assertTrue(listener_complete);
 assertEquals(4, break_count);