Unnecessary _now_ perhaps, but not unnecessary when lodash was written. In 2009, when underscore.js came out (from which lodash was a fork) Array.every() was not something you could rely on. Chrome just came out a year earlier (and didn't support Array.every until version 4) and half the world was on IE 6-7-8
For example, the code imports "copyArray", a 9LoC function that does exactly the same as the built-in Array.slice() would do.
Same goes for other imported helpers like "arrayEach", which could be replaced by the built-in Array.every().
It's basically a bunch of unnecessary polyfills for built-ins.