Remove empty "required" in schema

There are no required for WSLConf*, remove it instead of using empty
lists.

Co-authored-by: Didier Roche <didrocks@ubuntu.com>

autoinstall-system-setup-schema.json

@@ -83,7 +83,6 @@
                     "type": "boolean"
                 }
             },
-            "required": [],
             "additionalProperties": false
         },
         "wslconfadvanced": {
@@ -120,7 +119,6 @@
                     "type": "boolean"
                 }
             },
-            "required": [],
             "additionalProperties": false
         },
         "late-commands": {

system_setup/server/controllers/wslconfadvanced.py

@@ -49,7 +49,6 @@ class WSLConfigurationAdvancedController(SubiquityController):
             'automount': {'type': 'boolean'},
             'mountfstab': {'type': 'boolean'}
         },
-        'required': [],
         'additionalProperties': False,
     }
 

system_setup/server/controllers/wslconfbase.py

@@ -44,7 +44,6 @@ class WSLConfigurationBaseController(SubiquityController):
             'gen_host': {'type': 'boolean'},
             'gen_resolvconf': {'type': 'boolean'},
             },
-        'required': [],
         'additionalProperties': False,
         }