daemon: Remove daemon datastructure dump functionality

When sending SIGUSR1 to the daemon, it can crash because of a concurrent
map access panic, showing a stack trace involving dumpDaemon. It appears
it's not possible to recover from a concurrent map access panic. Since
it's important that SIGUSR1 not be a destructive operation, sadly the
best course of action I can think of is to remove this functionality.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

daemon/debugtrap_unix.go

@@ -22,12 +22,6 @@ func (d *Daemon) setupDumpStackTrap(root string) {
 			} else {
 				logrus.Infof("goroutine stacks written to %s", path)
 			}
-			path, err = d.dumpDaemon(root)
-			if err != nil {
-				logrus.WithError(err).Error("failed to write daemon datastructure dump")
-			} else {
-				logrus.Infof("daemon datastructure dump written to %s", path)
-			}
 		}
 	}()
 }