api-ref: Update note on flavor disabled property

This is not admin-only as suggested by the api-ref. In addition, there is
no mechanism available to disable flavors so this will always be false.

Change-Id: Ie1906366c8f141c6f6c58f21b0ff67eb827df4c8
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

api-ref/source/parameters.yaml

@@ -3043,7 +3043,9 @@ flavor_disabled:
   type: boolean
   description: |
     Whether or not the flavor has been administratively disabled.
-    This is typically only visible to administrative users.
+    This is an artifact of the legacy v2 API and will always be set to
+    ``false``. There is currently no way to disable a flavor and set this to
+    ``true``.
 flavor_disk:
   in: body
   required: true