Remove the 3.0.9 release from the 4.x NPM bundle

[ronyeh]

We had been keeping around the legacy version of VexFlow (v 3.0.9) in the releases/ directory.

This was because some old websites and old JSFiddles that depended on v3.0.9 linked directly to:
https://unpkg.com/vexflow/releases/vexflow-min.js

If we had removed the releases/ directly when we published v4.x, we would have broken those old sites. Even if we put v4.x into the releases/ directory (overwriting 3.0.9), we would have broken those old sites, since 4.x introduced breaking changes.

It's confusing that we ship the legacy version alongside the current one in the build/ directory.

4.x has been out long enough now (and we're working on 5.x). I think it's time we remove that releases/ folder. It's okay if those older JSFiddles break. :-)

I'll introduce a PR to remove the releases/ folder from the NPM package.

Originally posted by @ronyeh in #1630 (comment)