Abandon flavor-classes backlog spec

Scrubbing the backlog directory.

This spec has been here since 2015.

It is probably related to [1], but I haven't dug into that yet.  The
authors of either spec should feel free to modify this commit to
clarify.

[1] https://review.openstack.org/#/c/635408/

Change-Id: I1e5267a828133e9a6579a6790f2996c64a88fc8d

doc/source/specs/backlog/index.rst

@@ -24,8 +24,4 @@ Template:
 
 Approved (but not implemented) backlog specs:
 
-.. toctree::
-   :glob:
-   :maxdepth: 1
-
-   approved/*
+None currently

specs/abandoned/flavor-class.rst

@@ -8,6 +8,9 @@
 Flavor classes
 ==============
 
+.. note:: This spec was abandoned by efried on account of having been
+          sitting in the backlog directory since 2015.
+
 As an operator I would like to be able to define policy and quotas differently
 for different sets of hardware.
 
@@ -180,3 +183,5 @@ time.
      - Description
    * - Liberty
      - Introduced
+   * - Train
+     - Abandoned

specs/backlog/redirects

@@ -1,3 +1,4 @@
+approved/flavor-class.rst ../../abandoned/flavor-class.rst
 approved/instance-tasks.rst ../../abandoned/instance-tasks.rst
 approved/parallel-scheduler.rst ../../abandoned/parallel-scheduler.rst
 approved/same-instances-scheduling.rst ../../abandoned/same-instances-scheduling.rst