cmd/containerd: deduplicate config*.go

`config_linux.go` and `config_windows.go` are identical.

`config_unsupported.go` is also almost identical but enables debug logs by default.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

cmd/containerd/command/config_linux.go

@@ -17,21 +17,9 @@
 package command
 
 import (
-	"github.com/containerd/containerd/defaults"
 	srvconfig "github.com/containerd/containerd/services/server/config"
 )
 
 func defaultConfig() *srvconfig.Config {
-	return &srvconfig.Config{
-		Version: 1,
-		Root:    defaults.DefaultRootDir,
-		State:   defaults.DefaultStateDir,
-		GRPC: srvconfig.GRPCConfig{
-			Address:        defaults.DefaultAddress,
-			MaxRecvMsgSize: defaults.DefaultMaxRecvMsgSize,
-			MaxSendMsgSize: defaults.DefaultMaxSendMsgSize,
-		},
-		DisabledPlugins: []string{},
-		RequiredPlugins: []string{},
-	}
+	return platformAgnosticDefaultConfig()
 }