control/controlhttp: remove ClientConn.UntrustedUpgradeHeaders

It was just added and unreleased but we've decided to go a different route.

Details are in 5e9e57ecf5.

Updates #5972

Change-Id: I49016af469225f58535f63a9b0fbe5ab6a5bf304
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f