Mark `home_server` field deprecated

This is spelt wrong, and is redundant to user_id, so let's stop people using
it.

api/client-server/login.yaml

@@ -96,7 +96,6 @@ paths:
             application/json: {
                 "user_id": "@cheeky_monkey:matrix.org",
                 "access_token": "abc123",
-                "home_server": "matrix.org",
                 "device_id": "GHTYAJCE"
               }
           schema:
@@ -112,7 +111,12 @@ paths:
                   This access token can then be used to authorize other requests.
               home_server:
                 type: string
-                description: The hostname of the homeserver on which the account has been registered.
+                description: |-
+                  The server_name of the homeserver on which the account has been registered.
+
+                  **Deprecated**. Clients should extract the server_name from
+                  ``user_id`` if they require it. Note also that ``homeserver``
+                  is not spelt this way.
               device_id:
                 type: string
                 description: |-

api/client-server/registration.yaml

@@ -124,7 +124,6 @@ paths:
             application/json: {
                 "user_id": "@cheeky_monkey:matrix.org",
                 "access_token": "abc123",
-                "home_server": "matrix.org",
                 "device_id": "GHTYAJCE"
               }
           schema:
@@ -144,7 +143,12 @@ paths:
                   This access token can then be used to authorize other requests.
               home_server:
                 type: string
-                description: The hostname of the homeserver on which the account has been registered.
+                description: |-
+                  The server_name of the homeserver on which the account has been registered.
+
+                  **Deprecated**. Clients should extract the server_name from
+                  ``user_id`` if they require it. Note also that ``homeserver``
+                  is not spelt this way.
               device_id:
                 type: string
                 description: |-