Revert "Basic Python 3 support for testsuite driver (Trac #9184)"

This reverts commit 084d241b316bfa12e41fc34cae993ca276bf0730.

This is a possible culprit of Windows breakage reported at ghc-devs.
Restore spaces instead of tabs, caused by revert of Python 3

The git hook does not allow to reinsert tabs.