Removing Route's when none are defined. Fixes #39

```
$ acctests azurerm TestAccAzureRMRouteTable_removeRoute
=== RUN   TestAccAzureRMRouteTable_removeRoute
--- PASS: TestAccAzureRMRouteTable_removeRoute (93.89s)
PASS
ok      github.com/terraform-providers/terraform-provider-azurerm/azurerm    93.914s
```

azurerm/resource_arm_route_table.go

@@ -36,7 +36,6 @@ func resourceArmRouteTable() *schema.Resource {
 			"route": {
 				Type:     schema.TypeList,
 				Optional: true,
-				Computed: true,
 				Elem: &schema.Resource{
 					Schema: map[string]*schema.Schema{
 						"name": {
@@ -93,27 +92,22 @@ func resourceArmRouteTableCreate(d *schema.ResourceData, meta interface{}) error
 	resGroup := d.Get("resource_group_name").(string)
 	tags := d.Get("tags").(map[string]interface{})
 
+	routes, err := expandRouteTableRoutes(d)
+	if err != nil {
+		return fmt.Errorf("Error Expanding list of Route Table Routes: %+v", err)
+	}
+
 	routeSet := network.RouteTable{
 		Name:     &name,
 		Location: &location,
-		Tags:     expandTags(tags),
-	}
-
-	if _, ok := d.GetOk("route"); ok {
-		routes, routeErr := expandRouteTableRoutes(d)
-		if routeErr != nil {
-			return fmt.Errorf("Error Expanding list of Route Table Routes: %+v", routeErr)
-		}
-
-		if len(routes) > 0 {
-			routeSet.RouteTablePropertiesFormat = &network.RouteTablePropertiesFormat{
-				Routes: &routes,
-			}
-		}
+		RouteTablePropertiesFormat: &network.RouteTablePropertiesFormat{
+			Routes: &routes,
+		},
+		Tags: expandTags(tags),
 	}
 
 	_, createErr := client.CreateOrUpdate(resGroup, name, routeSet, make(chan struct{}))
-	err := <-createErr
+	err = <-createErr
 	if err != nil {
 		return err
 	}

azurerm/resource_arm_route_table_test.go

@@ -48,6 +48,35 @@ func TestAccAzureRMRouteTable_singleRoute(t *testing.T) {
 	})
 }
 
+func TestAccAzureRMRouteTable_removeRoute(t *testing.T) {
+	resourceName := "azurerm_route_table.test"
+	ri := acctest.RandInt()
+	config := testAccAzureRMRouteTable_singleRoute(ri, testLocation())
+	updatedConfig := testAccAzureRMRouteTable_basic(ri, testLocation())
+
+	resource.Test(t, resource.TestCase{
+		PreCheck:     func() { testAccPreCheck(t) },
+		Providers:    testAccProviders,
+		CheckDestroy: testCheckAzureRMRouteTableDestroy,
+		Steps: []resource.TestStep{
+			{
+				Config: config,
+				Check: resource.ComposeTestCheckFunc(
+					testCheckAzureRMRouteTableExists(resourceName),
+					resource.TestCheckResourceAttr(resourceName, "route.#", "1"),
+				),
+			},
+			{
+				Config: updatedConfig,
+				Check: resource.ComposeTestCheckFunc(
+					testCheckAzureRMRouteTableExists(resourceName),
+					resource.TestCheckResourceAttr(resourceName, "route.#", "0"),
+				),
+			},
+		},
+	})
+}
+
 func TestAccAzureRMRouteTable_disappears(t *testing.T) {
 	resourceName := "azurerm_route_table.test"
 	ri := acctest.RandInt()