The old-master branch will be the copy that contains all of the media files. The new master branch will be your source without the media files and will be a lot smaller. To push the new master branch to your git remote just execute:

git push origin -u master --force

Note -u will set the upstream branch for your local master to track the origin/master branch. You only need to do that once. --force will delete your remote master branch (if you have one) and force it to be your current master branch.

Once your new master branch is hosted you can just git push normally.

git push
#or if you want to be explicit
git push origin master

It's missing xlsx.
Just add:
**.[xX][lL][sS][xX]

Done :)