Revert "python: Simplify setup.py"

This reverts commit 8826fc2d7b4e59afdd8cea06891a0c43245340c5.

It seems that importing the module in setup.py is controversial at best,
as it will fail for users that don't have all dependencies
installed. This was the case in e.g. the Ubuntu autobuilder, so building
notmuch failed. The plan is to create an autogenerated setup.py that can
be used for version information.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>