Update the git-archive export options

The .gitattributes, .gitignore, .commit-template files do not need to be
present in packaged sources, as they are for people using the Git
repository.  People who download tarballs usually don't reimport into
Git -- they should just download the actual repositories.

Change-Id: I04d2ca436f5174c7820b42b6f5b2b9648c925fe3
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>