http: optimize debug function correctly

Exporting a variable that will be mutated later doesn't work.

Refs: https://github.com/nodejs/node/issues/37937

PR-URL: https://github.com/nodejs/node/pull/37966
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/_http_common.js

@@ -269,7 +269,6 @@ module.exports = {
   chunkExpression: /(?:^|\W)chunked(?:$|\W)/i,
   continueExpression: /(?:^|\W)100-continue(?:$|\W)/i,
   CRLF: '\r\n',
-  debug,
   freeParser,
   methods,
   parsers,