The `__future__` we relied on is now, where the 3 specific things are
all included [since Python 3.0](https://docs.python.org/3/library/__future__.html):
* absolute_import
* print_function
* unicode_literals
* division
These import statements are no-ops and are no longer necessary.
The library `six` provides compatibility between Python 2, and 3. It's no
longer necessary once we migrate of Python 2 completely.
Also remove any custom logic for Python 2 (the ones referenced by
a commentanyways).
https://bugs.swift.org/browse/SR-16025
SwiftVersionType needs 5 components, and ClangVersionType needs to match
SwiftVersionType because some build automation wants to mark the clang
version as being the same as the Swift version while generating version
numbers.
Fixes rdar://85508050
Having the test directory match the module we are testing means we can have scripts in the top level of utils/build_swift which can also have tests. As part of this re-structure the test utilties have been simplified somewhat and all tests no longer use a custom TestCase, rather the standard one exposed by the unittest module.
