This reverts commit 43e792bf55f3e53ae696b8480ba8fe73bac5bba0.

You can still override the track-level default template by adding a .meta/readme.go.tmpl for the exercise in question.

This removes the stray newline at the end of the generated READMEs.

We are working towards making exercises stand-alone—that is to say:
no more generating READMEs on the fly.

This will give maintainers more control over each individual exercise
README.

The template uses the Go text/template package, and the default templates
generate the exact same READMEs as we have been generating on the fly.