Python: Delete key wasn't actually persisting

The Python implementation of the PersistentStorageDelegate::SyncDeleteKey API
was not actually syncing the deleted key back to the underlying JSON
file, resulting in the deletion not actually 'sticking' despite passing
the storage audit.

src/controller/python/chip/storage/__init__.py

@@ -165,6 +165,7 @@ def GetSdkKey(self, key: str):
 
     def DeleteSdkKey(self, key: str):
         del(self.jsonData['sdk-config'][key])
+        self.Sync()
 
     def GetUnderlyingStorageAdapter(self):
         return self._storageAdapterObj