move most of cni/pkg to plugins/pkg: delete code staying in cni/pkg

This moves the following packages to this repository:
* ip
* ipam
* ns
* testutils
* utils

plugins/ipam/host-local/backend/allocator/allocator.go

@@ -20,9 +20,9 @@ import (
 	"net"
 	"os"
 
-	"github.com/containernetworking/cni/pkg/ip"
 	"github.com/containernetworking/cni/pkg/types"
 	"github.com/containernetworking/cni/pkg/types/current"
+	"github.com/containernetworking/plugins/pkg/ip"
 	"github.com/containernetworking/plugins/plugins/ipam/host-local/backend"
 )