Do not auto-remove content headers for body-less status codes

According to [RFC 2616 (HTTP/1.1 spec)](https://datatracker.ietf.org/doc/html/rfc2616#page-54) a `HEAD` request is supposed to return *exactly* the same entity-headers as a `GET` request but no body, imho responding to such a request with a 204 status code seems reasonable (if not ideal), thus we should not remove any headers but only ensure that no body is sent.

Author: LJ1102

lib/response.js

@@ -209,23 +209,19 @@ res.send = function send(body) {
   // freshness
   if (req.fresh) this.statusCode = 304;
 
-  // strip irrelevant headers
-  if (204 === this.statusCode || 304 === this.statusCode) {
-    this.removeHeader('Content-Type');
-    this.removeHeader('Content-Length');
-    this.removeHeader('Transfer-Encoding');
-    chunk = '';
-  }
-
   // alter headers for 205
   if (this.statusCode === 205) {
     this.set('Content-Length', '0')
     this.removeHeader('Transfer-Encoding')
     chunk = ''
   }
 
-  if (req.method === 'HEAD') {
-    // skip body for HEAD
+  if (
+    req.method === 'HEAD' ||
+    204 === this.statusCode ||
+    304 === this.statusCode
+  ) {
+    // skip body
     this.end();
   } else {
     // respond