refactor: remove getHeaderNames() polyfill and refactor clearHeaders()

`ServerResponse.getHeaderNames()` is available since Node v7.7.0

Author: Phillip9587

HISTORY.md

@@ -4,6 +4,7 @@ unreleased
   * deps: 
     * `fresh@^2.0.0` 
     * removed `destroy`
+  * remove `getHeaderNames()` polyfill and refactor `clearHeaders()`
 
 1.1.0 / 2024-09-10
 ==================

index.js

@@ -775,10 +775,8 @@ SendStream.prototype.setHeader = function setHeader (path, stat) {
  */
 
 function clearHeaders (res) {
-  var headers = getHeaderNames(res)
-
-  for (var i = 0; i < headers.length; i++) {
-    res.removeHeader(headers[i])
+  for (const header of res.getHeaderNames()) {
+    res.removeHeader(header)
   }
 }
 
@@ -886,20 +884,6 @@ function decode (path) {
   }
 }
 
-/**
- * Get the header names on a response.
- *
- * @param {object} res
- * @returns {array[string]}
- * @private
- */
-
-function getHeaderNames (res) {
-  return typeof res.getHeaderNames !== 'function'
-    ? Object.keys(res._headers || {})
-    : res.getHeaderNames()
-}
-
 /**
  * Determine if emitter has listeners of a given type.
  *