So just some background, browserify is a bundler that converts JS written for node into JS that works in the browser, it includes JS versions of standard library in case you try to bundle libraries that use the standard library. These standard library shims are also used by webpack.
As for diffie-helmen in specific, It's performance is not great so I highly doubt much/any code was using it, much of the stuff using diffie-helmen in node is connected to tls implementation and thus isn't going to be part of something being bundled in the browser so if you have questions on it you could probably go ahead and just remove it in favor of a stub package.
