gpython: Kill stray `import sys`

sys is imported in the beginning of main, so there is no need to import
it the second time in the middle of main. The bug was there since
gpython day1 - since 32a21d5b (gpython: Python interpreter with support
for lightweight threads).

gpython/__init__.py

@@ -181,7 +181,6 @@ def main():
         exe = exe[:-len('-script.py')]
         exe = exe + '.exe'
 
-    import sys
     sys.executable  = exe
     sys.version    += (' [GPython %s]' % golang.__version__)