Remove asynchronous chdir callback

Author: stilley2

nipype/pipeline/plugins/multiproc.py

@@ -146,8 +146,6 @@ def __init__(self, plugin_args=None):
         self._stats = None
 
     def _async_callback(self, args):
-        # Make sure runtime is not left at a dubious working directory
-        os.chdir(self._cwd)
         result = args.result()
         self._taskresult[result['taskid']] = result