Fix legacy template entity_id field in migration

homeassistant/components/template/helpers.py

@@ -12,6 +12,7 @@
 from homeassistant.components import blueprint
 from homeassistant.config_entries import ConfigEntry
 from homeassistant.const import (
+    ATTR_ENTITY_ID,
     CONF_ENTITY_PICTURE_TEMPLATE,
     CONF_FRIENDLY_NAME,
     CONF_ICON,
@@ -133,6 +134,9 @@ def rewrite_legacy_to_modern_config(
     """Rewrite legacy config."""
     entity_cfg = {**entity_cfg}
 
+    # Remove deprecated entity_id field from legacy syntax
+    entity_cfg.pop(ATTR_ENTITY_ID, None)
+
     for from_key, to_key in itertools.chain(
         LEGACY_FIELDS.items(), extra_legacy_fields.items()
     ):

tests/components/template/test_helpers.py

@@ -832,13 +832,14 @@ async def test_legacy_deprecation(
                     "sensors": {
                         "some_sensor": {
                             "friendly_name": "Sensor",
+                            "entity_id": "sensor.some_sensor",
                             "device_class": "timestamp",
                             "value_template": "{{ now().isoformat() }}",
                         }
                     },
                 },
             },
-            ["device_class: timestamp"],
+            ["device_class: timestamp", "entity_id: sensor.some_sensor"],
         ),
     ],
 )