Revert r88503 as Benjamin's request.

Lib/lib2to3/__main__.py

-import sys
-from .main import main
-
-sys.exit(main("lib2to3.fixes"))

Tools/scripts/2to3

 #!/usr/bin/env python
-import runpy
+import sys
+from lib2to3.main import main
 
-runpy.run_module('lib2to3', run_name='__main__', alter_sys=True)
+sys.exit(main("lib2to3.fixes"))