Remove extra parameter for token auth

The /v3/auth/token API's response body doesn't contain
extra at all.
It has been removed here: https://review.openstack.org/#/c/249480/

This patch remove the "extra" from api-ref to avoid misleading.

Change-Id: I3d41c022835bc43e5bf46d1d522dfcdcc0a8922e

api-ref/source/v3/authenticate-v3.inc

@@ -142,7 +142,6 @@ Response Parameters
    - methods: auth_methods_passwd
    - expires_at: expires_at
    - token: token
-   - extras: extras
    - user: user
    - audit_ids: audit_ids
    - issued_at: issued_at
@@ -211,7 +210,6 @@ Response Parameters
    - project: project
    - issued_at: issued_at
    - catalog: catalog
-   - extras: extras
    - user: user
    - audit_ids: audit_ids
    - interface: endpoint_interface
@@ -275,7 +273,6 @@ Response Parameters
    - roles: roles
    - expires_at: expires_at
    - token: token
-   - extras: extras
    - user: user
    - audit_ids: audit_ids
    - issued_at: issued_at
@@ -476,7 +473,6 @@ Response Parameters
    - expires_at: expires_at
    - project: project
    - catalog: catalog
-   - extras: extras
    - roles: roles
    - audit_ids: audit_ids
    - issued_at: issued_at

api-ref/source/v3/parameters.yaml

@@ -849,12 +849,6 @@ explicit_unscoped_string:
   in: body
   required: false
   type: string
-extras:
-  description: |
-    A set of metadata key and value pairs, if any.
-  in: body
-  required: true
-  type: object
 group:
   description: |
     A ``group`` object, containing:

api-ref/source/v3/samples/admin/auth-password-explicit-unscoped-response.json

@@ -4,7 +4,6 @@
             "password"
         ],
         "expires_at": "2015-11-09T01:42:57.527363Z",
-        "extras": {},
         "user": {
             "domain": {
                 "id": "default",

api-ref/source/v3/samples/admin/auth-password-project-scoped-response.json

@@ -385,7 +385,6 @@
                 "name": "heat-cfn"
             }
         ],
-        "extras": {},
         "user": {
             "domain": {
                 "id": "default",

api-ref/source/v3/samples/admin/auth-password-unscoped-response.json

@@ -4,7 +4,6 @@
             "password"
         ],
         "expires_at": "2015-11-06T15:32:17.893769Z",
-        "extras": {},
         "user": {
             "domain": {
                 "id": "default",

api-ref/source/v3/samples/admin/auth-token-scoped-response.json

@@ -385,7 +385,6 @@
                 "name": "swift"
             }
         ],
-        "extras": {},
         "user": {
             "domain": {
                 "id": "default",

api-ref/source/v3/samples/admin/auth-token-unscoped-response.json

@@ -4,7 +4,6 @@
             "token"
         ],
         "expires_at": "2015-11-05T22:00:11.000000Z",
-        "extras": {},
         "user": {
             "domain": {
                 "id": "default",