Abandon instance-tasks backlog spec

Scrubbing the backlog directory.

This spec has been here since 2015.

The original authors should feel free to modify or downvote this commit
if the spec should continue to be considered for implementation now or
in the future.

Change-Id: Idec4df4b3fe689d73da4786993aaf8aa13c2dbf0

specs/abandoned/index.rst

@@ -25,4 +25,4 @@ real.
    :glob:
    :maxdepth: 1
 
-   *
+   *

specs/abandoned/instance-tasks.rst

@@ -8,6 +8,9 @@
 Instance tasks - A short history and primer
 ===========================================
 
+.. note:: This spec was abandoned by efried on account of having been
+          sitting in the backlog directory since 2015.
+
 This starts as a story about exposing errors to users.
 
 From very early on, if not the beginning, the Nova API has had a concept of an
@@ -219,3 +222,5 @@ time.
      - Description
    * - Liberty
      - Introduced
+   * - Train
+     - Abandoned

specs/backlog/redirects

@@ -1 +1,2 @@
+approved/instance-tasks.rst ../../abandoned/instance-tasks.rst
 approved/parallel-scheduler.rst ../../abandoned/parallel-scheduler.rst