fix: stop manually dropping dhcp6 key in integration test (#5267)

This reverts the temporary changed introduced by PR #4855 that
manually dropped the "dhcp6" key from the post_network yaml
in the integration test "test_clean_boot_of_upgraded_package"

tests/integration_tests/test_upgrade.py

@@ -13,7 +13,6 @@
     FOCAL,
     IS_UBUNTU,
     MANTIC,
-    NOBLE,
 )
 from tests.integration_tests.util import verify_clean_log
 
@@ -144,28 +143,15 @@ def test_clean_boot_of_upgraded_package(session_cloud: IntegrationCloud):
                 assert post_json["v1"]["datasource"].startswith(
                     "DataSourceAzure"
                 )
-        if PLATFORM in ["gce", "qemu"] and CURRENT_RELEASE < NOBLE:
-            # GCE regenerates network config per boot AND
-            # GCE uses fallback config AND
-            # #4474 changed fallback configuration.
-            # Once the baseline includes #4474, this can be removed
-            pre_network = yaml.load(pre_network, Loader=yaml.Loader)
-            post_network = yaml.load(post_network, Loader=yaml.Loader)
-            for values in post_network["network"]["ethernets"].values():
-                values.pop("dhcp6")
-            assert yaml.dump(pre_network) == yaml.dump(post_network)
+        if CURRENT_RELEASE < MANTIC:
+            # Assert the full content is preserved including header comment
+            # since cloud-init writes the file directly and does not use
+            # netplan API to write 50-cloud-init.yaml.
+            assert pre_network == post_network
         else:
-            if CURRENT_RELEASE < MANTIC:
-                # Assert the full content is preserved including header comment
-                # since cloud-init writes the file directly and does not use
-                # netplan API to write 50-cloud-init.yaml.
-                assert pre_network == post_network
-            else:
-                # Mantic and later Netplan API is used and doesn't allow
-                # cloud-init to write header comments in network config
-                assert yaml.safe_load(pre_network) == yaml.safe_load(
-                    post_network
-                )
+            # Mantic and later Netplan API is used and doesn't allow
+            # cloud-init to write header comments in network config
+            assert yaml.safe_load(pre_network) == yaml.safe_load(post_network)
 
         # Calculate and log all the boot numbers
         pre_analyze_totals = [