tcp guide: remove section on metadata based tcp matches
tcp guide: remove section on metadata based tcp matches

In commit c7bb1d62 (#808), we documented how the tcp route match
extension point can be used for metadata based tcp matching.

Soon after, in commit e3450f77 (#829), this extension point was
removed, but the docs remained.

Remove this section to reflect the current state of the API.

istio/gateway-api,istio/gateway-api,istio/gateway-api