remove expired notes for Multi Store feature

The Multi Store feature is stable for server versions, need delete the EXPERIMENTAL notes in api guide.

Change-Id: Ifff797387ec06e8a1c0da13ebd722df0b993d672

Author: anguoming

api-ref/source/v2/discovery.inc

@@ -68,11 +68,6 @@ List stores
 A multiple store backend support is introduced in the Rocky release
 as a part of the EXPERIMENTAL Image API v2.8.
 
-.. note:: The Multi Store feature is introduced as EXPERIMENTAL in Rocky and
-          its use in production systems is currently **not supported**.
-          The feature is being finalized during the Train development
-          cycle and is expected to be fully supported in Image API v2.9.
-
 In version 2.7 of the API, this call will return a 404 (Not Found).
 Use the :ref:`API versions call <versions-call>` to determine
 what API versions are available in your cloud.

api-ref/source/v2/images-data.inc

@@ -31,12 +31,6 @@ header.  If the store identifier specified is not recognized, a 400 (Bad
 Request) response is returned.  When the header is not present, the image
 data is placed into the default backing store.
 
-.. note:: The Multi Store feature is introduced as EXPERIMENTAL in Rocky and
-          its use in production systems is currently **not supported**.
-          However we encourage people to use this feature for testing
-          purposes and report the issues so that we can make it stable and
-          fully supported in Stein release.
-
 * Store identifiers are site-specific.  Use the :ref:`Store
   Discovery <store-discovery-call>` call to determine what
   stores are available in a particular cloud.

api-ref/source/v2/images-images-v2.inc

@@ -159,12 +159,6 @@ new header ``OpenStack-image-store-ids`` which contains the list of
 available stores will be included in response. This header is only
 included if multiple backend stores are supported.
 
-.. note:: The Multi Store feature is introduced as EXPERIMENTAL in Rocky and
-          its use in production systems is currently **not supported**.
-          However we encourage people to use this feature for testing
-          purposes and report the issues so that we can make it stable and
-          fully supported in Stein release.
-
 The response body contains the new image entity.
 
 Synchronous Postconditions