A symlink is the term symbolic link , which is basically an extended shortcut. Symlinks are created during the github build process. They point to the files in your assembly. If you are not using the file to create your site, you can safely delete it.
If you need a symlinked file to create your site, make sure that the file or directory it refers to is in your repository.
To delete a file in git, use:
find . -type l -exec git rm --cached {} \;