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: I8d3eb36583d0fb6a3622f34427819fbc39b1b9ff
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>