hubble-relay: remove dial-timeout following deprecation in 1.17

Follow-up to: https://github.com/cilium/cilium/pull/36027

While refactoring deprecated calls to `grpc.DialContext` with `grpc.NewClient`, we also deprecated the `--dial-timeout` flag and `.Values.hubble.relay.dialTimeout` helm value since creating a client no longer requires dialing (it is now handled internally by the grpc runtime).

For 1.18, we should remove the flag and helm value.