Remove overridden references to examples/minimal_pdu.json and add the missing room_id field. (#1454)

The syntax is incorrect and would require to use allOf
because a $ref can't have siblings.
However the only field not overwritten of that definition is room_id,
so we include it instead of the $ref

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

data/api/server-server/knocks.yaml

@@ -129,7 +129,7 @@ paths:
             application/json: {
               "room_version": "7",
               "event": {
-                "$ref": "examples/minimal_pdu.json",
+                "room_id": "!somewhere:example.org",
                 "type": "m.room.member",
                 "state_key": "@someone:example.org",
                 "origin": "example.org",
@@ -264,7 +264,7 @@ paths:
               - type
               - content
           example: {
-            "$ref": "examples/minimal_pdu.json",
+            "room_id": "!somewhere:example.org",
             "type": "m.room.member",
             "state_key": "@someone:example.org",
             "origin": "example.org",