Removed (*App).Shutdown and updated all references. (#15088)

app/app_iface.go

@@ -83,10 +83,6 @@ type AppIface interface {
 	CreateUser(user *model.User) (*model.User, *model.AppError)
 	// Creates and stores FileInfos for a post created before the FileInfos table existed.
 	MigrateFilenamesToFileInfos(post *model.Post) []*model.FileInfo
-	// DO NOT CALL THIS.
-	// This is to avoid having to change all the code in cmd/mattermost/commands/* for now
-	// shutdown should be called directly on the server
-	Shutdown()
 	// DefaultChannelNames returns the list of system-wide default channel names.
 	//
 	// By default the list will be (not necessarily in this order):