chore: Remove h2mux code

Some more legacy h2mux code to be cleaned up and moved out of the way.
The h2mux.Header used in the serialization for http2 proxied headers is moved to connection module. Additionally, the booleanfuse structure is also moved to supervisor as it is also needed. Both of these structures could be evaluated later for removal/updates, however, the intent of the proposed changes here is to remove the dependencies on the h2mux code and removal.

Approved-by: Chung-Ting Huang <chungting@cloudflare.com>
Approved-by: Luis Neto <lneto@cloudflare.com>
Approved-by: Gonçalo Garcia <ggarcia@cloudflare.com>

MR: https://gitlab.cfdata.org/cloudflare/tun/cloudflared/-/merge_requests/1576

connection/errors.go

@@ -2,7 +2,6 @@ package connection
 
 import (
 	"github.com/cloudflare/cloudflared/edgediscovery"
-	"github.com/cloudflare/cloudflared/h2mux"
 	tunnelpogs "github.com/cloudflare/cloudflared/tunnelrpc/pogs"
 )
 
@@ -71,8 +70,6 @@ func isHandshakeErrRecoverable(err error, connIndex uint8, observer *Observer) b
 	switch err.(type) {
 	case edgediscovery.DialError:
 		log.Error().Msg("Connection unable to dial edge")
-	case h2mux.MuxerHandshakeError:
-		log.Error().Msg("Connection handshake with edge server failed")
 	default:
 		log.Error().Msg("Connection failed")
 		return false