Clean up PUT /directory/room

Fixes https://github.com/matrix-org/matrix-doc/issues/933

The issue references two problems: a `roomInfo` and lack of a `room_id`. It appears the `room_id` has been fixed since reporting, however the `roomInfo` remained (and is now fixed).

api/client-server/directory.yaml

@@ -41,7 +41,7 @@ paths:
           required: true
           x-example: "#monkeys:matrix.org"
         - in: body
-          name: roomInfo
+          name: body
           description: Information about this room alias.
           required: true
           schema:
@@ -50,6 +50,7 @@ paths:
               room_id:
                 type: string
                 description: The room ID to set.
+            required: ['room_id']
             example: {
               "room_id": "!abnjk1jdasj98:capuchins.com"
             }
@@ -57,8 +58,7 @@ paths:
         200:
           description: The mapping was created.
           examples:
-            application/json: {
-              }
+            application/json: {}
           schema:
             type: object
         409: