Remove CommonJS entry point

[Borewit]

loadMusicMetadata() no longer available.
load-esm can be used instead.

Replace

import {loadMusicMetadata} from 'music-metadata';

(async () => {
  const mm = await loadMusicMetadata();
})();

with:

npm install load-esm

import {loadEsm} from 'load-esm';

(async () => {
  const mm = await loadEsm<typeof import('music-metadata')>('music-metadata');
})();

Benefits:

• One generic shared solution which works for importing any pure ESM project
• Avoid CommonJS and ESM typings getting mixed up

[coveralls]

coverage: 97.002% (-0.003%) from 97.005%
when pulling c7688d7 on remove-cjs-entry-point
into ac4119c on master.