revert https://github.com/OffchainLabs/prysm/pull/16100 (#16139)

This PR reverts https://github.com/OffchainLabs/prysm/pull/16100.

**What type of PR is this?**
Bug fix


**What does this PR do? Why is it needed?**
This PR reverts https://github.com/OffchainLabs/prysm/pull/16100 as that
PR deprecates mplex but other implementations only support mplex for
now..


**Which issues(s) does this PR fix?**

Fixes #

**Other notes for review**

**Acknowledgements**

- [x] I have read
[CONTRIBUTING.md](https://github.com/prysmaticlabs/prysm/blob/develop/CONTRIBUTING.md).
- [x] I have included a uniquely named [changelog fragment
file](https://github.com/prysmaticlabs/prysm/blob/develop/CONTRIBUTING.md#maintaining-changelogmd).
- [x] I have added a description with sufficient context for reviewers
to understand this PR.
- [x] I have tested that my changes work as expected and I added a
testing plan to the PR description (if applicable).

cmd/beacon-chain/main.go

@@ -131,7 +131,6 @@ var appFlags = []cli.Flag{
 	debug.MutexProfileFractionFlag,
 	cmd.LogFileName,
 	cmd.EnableUPnPFlag,
-	cmd.EnableAutoNATFlag,
 	cmd.ConfigFileFlag,
 	cmd.ChainConfigFileFlag,
 	cmd.GrpcMaxCallRecvMsgSizeFlag,

cmd/beacon-chain/usage.go

@@ -82,7 +82,6 @@ var appHelpFlagGroups = []flagGroup{
 		Flags: []cli.Flag{
 			cmd.BootstrapNode,
 			cmd.EnableUPnPFlag,
-			cmd.EnableAutoNATFlag,
 			cmd.NoDiscovery,
 			cmd.P2PAllowList,
 			cmd.P2PDenyList,