Remove old Serialization enums (#52183)

This aren't used anymore -- these were initially part of AIP-44 but were missed during cleanup

Author: kaxil

airflow-core/src/airflow/serialization/enums.py

@@ -62,16 +62,10 @@ class DagAttributeTypes(str, Enum):
     ASSET_REF = "asset_ref"
     ASSET_UNIQUE_KEY = "asset_unique_key"
     ASSET_ALIAS_UNIQUE_KEY = "asset_alias_unique_key"
-    BASE_JOB = "Job"
-    TASK_INSTANCE = "task_instance"
-    DAG_RUN = "dag_run"
-    DAG_MODEL = "dag_model"
-    LOG_TEMPLATE = "log_template"
     CONNECTION = "connection"
     TASK_CONTEXT = "task_context"
     ARG_NOT_SET = "arg_not_set"
     TASK_CALLBACK_REQUEST = "task_callback_request"
     DAG_CALLBACK_REQUEST = "dag_callback_request"
     TASK_INSTANCE_KEY = "task_instance_key"
-    TRIGGER = "trigger"
     DEADLINE_ALERT = "deadline_alert"