Remove 'room_id' field from `m.typing`, `m.receipt` and `m.fully_read` examples and schema (#3679)

The spec had an erroneous `room_id` field in a m.typing EDU entry of /sync, `m.read` receipts in `/sync`, and `m.fully_read` room account data objects in the spec. None of these are necessary nor used in practice.

Checking part of the ecosystem for whether clients look for, or homeservers include, these room_id fields, I found that:

    Element does not require them, nor does Synapse include them.
    Ruma does not include them.
    Dendrite does not include them.
    nheko/mtxclient does not look for them.

This change removes room_id from the example and OpenAPI schema in each case mentioned above. It only affects the Client-Server spec - the Server-Server spec text remains unchanged.

The field was initially introduced in 0f28f83.

changelogs/client_server/newsfragments/3679.clarification

@@ -0,0 +1 @@
+Remove erroneous `room_id` field from examples of `m.read`, `m.typing` in `/sync` and `m.fully_read` in room account data.

data/event-schemas/examples/core/room_edu.json

@@ -1,4 +1,3 @@
 {
-    "$ref": "event.json",
-    "room_id": "!jEsUZKDJdhlrceRyVU:example.org"
+    "$ref": "event.json"
 }

data/event-schemas/examples/m.fully_read.yaml

@@ -1,7 +1,6 @@
 {
   "$ref": "core/event.json",
   "type": "m.fully_read",
-  "room_id": "!somewhere:example.org",
   "content": {
     "event_id": "$someplace:example.org"
   }

data/event-schemas/schema/m.fully_read.yaml

@@ -19,11 +19,7 @@
         "type": {
             "type": "string",
             "enum": ["m.fully_read"]
-        },
-        "room_id": {
-            "type": "string",
-            "description": "The room ID the read marker applies to."
         }
     },
-    "required": ["type", "room_id", "content"]
+    "required": ["type", "content"]
 }

data/event-schemas/schema/m.receipt.yaml

@@ -42,10 +42,7 @@
         "type": {
             "type": "string",
             "enum": ["m.receipt"]
-        },
-        "room_id": {
-            "type": "string"
         }
     },
-    "required": ["room_id", "type", "content"]
+    "required": ["type", "content"]
 }

data/event-schemas/schema/m.typing.yaml

@@ -22,10 +22,7 @@
         "type": {
             "type": "string",
             "enum": ["m.typing"]
-        },
-        "room_id": {
-            "type": "string"
         }
     },
-    "required": ["type", "room_id", "content"]
+    "required": ["type", "content"]
 }