python: Get rid of version arg in OptionParser constructor.

This will report that gem5 is version 2.0, which is WILDLY out of date.
There are other ways of reporting the version of gem5 which are actually
kept up to date.

Change-Id: Ie09cdc8f3ef59696fe197c3491db102bda41ade0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/50708
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/m5/main.py

@@ -45,7 +45,6 @@ import sys
 __all__ = [ 'options', 'arguments', 'main' ]
 
 usage="%prog [gem5 options] script.py [script options]"
-version="%prog 2.0"
 brief_copyright=\
     "gem5 is copyrighted software; use the --copyright option for details."
 
@@ -65,8 +64,7 @@ def parse_options():
     from . import config
     from .options import OptionParser
 
-    options = OptionParser(usage=usage, version=version,
-                           description=brief_copyright)
+    options = OptionParser(usage=usage, description=brief_copyright)
     option = options.add_option
     group = options.set_group