Remove plugin deprecated 'UseTunnelDeprecated'

Signed-off-by: George Jenkins <gvjenkins@gmail.com>

pkg/plugin/plugin.go

@@ -132,12 +132,6 @@ type Metadata struct {
 	// Downloaders field is used if the plugin supply downloader mechanism
 	// for special protocols.
 	Downloaders []Downloaders `json:"downloaders"`
-
-	// UseTunnelDeprecated indicates that this command needs a tunnel.
-	// Setting this will cause a number of side effects, such as the
-	// automatic setting of HELM_HOST.
-	// DEPRECATED and unused, but retained for backwards compatibility with Helm 2 plugins. Remove in Helm 4
-	UseTunnelDeprecated bool `json:"useTunnel,omitempty"`
 }
 
 // Plugin represents a plugin.