http2: remove no longer userful options.selectPadding

This is a followup cleanup on a previous PR. Current source code and doc
explicitly states that `selectPadding` has been removed for all exports.

Refs: #29144
Refs: https://nodejs.org/api/http2.html

Author: hkleungai

lib/internal/http2/core.js

@@ -244,7 +244,6 @@ const kPendingRequestCalls = Symbol('kPendingRequestCalls');
 const kProceed = Symbol('proceed');
 const kRemoteSettings = Symbol('remote-settings');
 const kRequestAsyncResource = Symbol('requestAsyncResource');
-const kSelectPadding = Symbol('select-padding');
 const kSentHeaders = Symbol('sent-headers');
 const kSentTrailers = Symbol('sent-trailers');
 const kServer = Symbol('server');
@@ -1082,8 +1081,6 @@ function setupHandle(socket, type, options) {
   const handle = new binding.Http2Session(type);
   handle[kOwner] = this;
 
-  if (typeof options.selectPadding === 'function')
-    this[kSelectPadding] = options.selectPadding;
   handle.consume(socket._handle);
   handle.ongracefulclosecomplete = this[kMaybeDestroy].bind(this, null);