pool: Fix mover leak

Motivation:

A regression causes the pool to leak movers when these are cancelled while
still being queued.

Modification:

Remove the mover from the deduplication map.

Result:

Fixed a regression that caused pools to leak movers if these are cancelled
while still being queued.

Target: trunk
Require-notes: yes
Require-book: no
Request: 2.16
Request: 2.15
Request: 2.14
Request: 2.13
Acked-by: Paul Millar <paul.millar@desy.de>
Acked-by: Albert Rossi <arossi@fnal.gov>

Reviewed at https://rb.dcache.org/r/9477/

(cherry picked from commit 9b7b679)

modules/dcache/src/main/java/org/dcache/pool/classic/MoverRequestScheduler.java

@@ -309,6 +309,7 @@ public void failed(Throwable exc, Void attachment) {
                     private void release() {
                         request.done();
                         _jobs.remove(request.getId());
+                        _moverByRequests.remove(request.getDoorUniqueId());
                     }
 
                 });