http2: reduce require calls in http2/core

This commit removes unnecesary requires of http and internal/util in
http2/core.js

Backport-PR-URL: #22850
PR-URL: #20422
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

Author: danbev

lib/internal/http2/core.js

@@ -23,9 +23,12 @@ const { onServerStream,
         Http2ServerResponse,
 } = require('internal/http2/compat');
 const { utcDate } = require('internal/http');
-const { promisify } = require('internal/util');
+const {
+  promisify,
+  customInspectSymbol: kInspect
+} = require('internal/util');
 const { isArrayBufferView } = require('internal/util/types');
-const { _connectionListener: httpConnectionListener } = require('http');
+const { _connectionListener: httpConnectionListener } = http;
 const { createPromise, promiseResolve } = process.binding('util');
 const debug = util.debuglog('http2');
 
@@ -67,7 +70,6 @@ const { constants, nameForErrorCode } = binding;
 const NETServer = net.Server;
 const TLSServer = tls.Server;
 
-const kInspect = require('internal/util').customInspectSymbol;
 const { kIncomingMessage } = require('_http_common');
 const { kServerResponse } = require('_http_server');