Drop broken/no-op proxyconfig.EndpointsHandler implementations

Because the proxy.Provider interface included
proxyconfig.EndpointsHandler, all the backends needed to
implement its methods. But iptables, ipvs, and winkernel implemented
them as no-ops, and metaproxier had an implementation that wouldn't
actually work (because it couldn't handle Services with no active
Endpoints).

Since Endpoints processing in kube-proxy is deprecated (and can't be
re-enabled unless you're using a backend that doesn't support
EndpointSlice), remove proxyconfig.EndpointsHandler from the
definition of proxy.Provider and drop all the useless implementations.

pkg/proxy/types.go

@@ -28,7 +28,6 @@ import (
 
 // Provider is the interface provided by proxier implementations.
 type Provider interface {
-	config.EndpointsHandler
 	config.EndpointSliceHandler
 	config.ServiceHandler
 	config.NodeHandler