Here is a super simple package.js script:

var iconv = require('iconv-lite');

console.warn('We are not using iconv at all!');

As you can see, iconv is never used.

Using the CLI command of the documentation browserify -p [common-shakeify -v] package.js > bundle.js, the final bundle is not tree-shaked. There is only one common-shake comment in the generated bundle:

/* common-shake removed: exports.byteLength = */

I expect the whole iconv module to be removed since it is not used at all.