Fix of 0022630: EDF 8445 - using multiprocessing with the Python console of SALOME...

Fix of 0022630: EDF 8445 - using multiprocessing with the Python console of SALOME 7.4.0.
Copying of main dictionary was added by 'ad3a201' commit in order to have a new context of Python interpreter for each study, but it leads to the situation that '__main__' module in sys.modules dictionary is not updated with a new functions and variables.
Now dictionary copying has been removed to fix the mentioned bug, but we have a common Python context for all studies in the Salome session.