command/graph: Remove no-op state unlock

The graph command never locks the state, so this unlock operation was a
no-op and is a bit of a red herring. Remove it.

command/graph.go

@@ -111,13 +111,6 @@ func (c *GraphCommand) Run(args []string) int {
 		return 1
 	}
 
-	defer func() {
-		err := opReq.StateLocker.Unlock(nil)
-		if err != nil {
-			c.Ui.Error(err.Error())
-		}
-	}()
-
 	// Determine the graph type
 	graphType := terraform.GraphTypePlan
 	if plan != nil {