remove phantomjs

https://github.com/crypto-browserify/randombytes/blob/f18ded32b209f0d4c637608a11ae042ae96b4c2e/browser.js#L25-L26

Phantomjs is suspended and not being worked on any longer.
Phantomjs have never been a browser that anyone is using due to lack of any UI. it was solo used for testing and scripting automation, so it's very unpopular
ppl start using headless chrome or firefox nowdays

Inspect browser.js at lines 25-26, starting with the PhantomJS reference identified in the issue. Remove the obsolete PhantomJS support and run the project's existing tests to confirm the browser build still works without it.

索引モデルが issue の本文から書いたものです。