remove obsolete pywikibot.stopme() at the end of some scripts.

In core branch pywikibot.stopme() is called by atexit library.
The function is executed upon normal program termination. This
patch prohibits executing it twice.

Change-Id: I6759a6ad476e4ea6999b987ee1d2057d6165f061
Merge "remove obsolete pywikibot.stopme() at the end of some scripts."