lib: remove unused join from internal/util

lib/internal/util.js

@@ -385,21 +385,6 @@ function promisify(original) {
 
 promisify.custom = kCustomPromisifiedSymbol;
 
-// The built-in Array#join is slower in v8 6.0
-function join(output, separator) {
-  let str = '';
-  if (output.length !== 0) {
-    const lastIndex = output.length - 1;
-    for (let i = 0; i < lastIndex; i++) {
-      // It is faster not to use a template string here
-      str += output[i];
-      str += separator;
-    }
-    str += output[lastIndex];
-  }
-  return str;
-}
-
 // As of V8 6.6, depending on the size of the array, this is anywhere
 // between 1.5-10x faster than the two-arg version of Array#splice()
 function spliceOne(list, index) {
@@ -579,7 +564,6 @@ module.exports = {
   getSystemErrorName,
   isError,
   isInsideNodeModules,
-  join,
   lazyDOMException,
   lazyDOMExceptionClass,
   normalizeEncoding,