fix: bug on google_compute_router_nat where changes to auto_network_tier are always showed after initial apply (#14051) (#23190)

[upstream:b39e4e48beccd7cfdd6594f4002fc84db3d27589]

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/14051.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+compute: fix `google_compute_router_nat` where changes to `auto_network_tier` are always showed after initial apply
+```

google/services/compute/resource_compute_router_nat.go

@@ -973,9 +973,6 @@ func resourceComputeRouterNatRead(d *schema.ResourceData, meta interface{}) erro
 	if err := d.Set("type", flattenNestedComputeRouterNatType(res["type"], d, config)); err != nil {
 		return fmt.Errorf("Error reading RouterNat: %s", err)
 	}
-	if err := d.Set("auto_network_tier", flattenNestedComputeRouterNatAutoNetworkTier(res["autoNetworkTier"], d, config)); err != nil {
-		return fmt.Errorf("Error reading RouterNat: %s", err)
-	}
 
 	return nil
 }
@@ -1616,10 +1613,6 @@ func flattenNestedComputeRouterNatType(v interface{}, d *schema.ResourceData, co
 	return v
 }
 
-func flattenNestedComputeRouterNatAutoNetworkTier(v interface{}, d *schema.ResourceData, config *transport_tpg.Config) interface{} {
-	return v
-}
-
 func expandNestedComputeRouterNatName(v interface{}, d tpgresource.TerraformResourceData, config *transport_tpg.Config) (interface{}, error) {
 	return v, nil
 }