devmapper: Do not add back device into hash map if meta file removal failed

When we are deleting a device, we also delete associated metadata file. If
that file removal fails, we are adding back the device in in-memory
table. I really can't see what's the point. When next lookup takes place
it will be automatically loaded if need be. Remove that code.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

daemon/graphdriver/devmapper/deviceset.go

@@ -814,9 +814,6 @@ func (devices *DeviceSet) deleteDevice(info *DevInfo) error {
 	devices.devicesLock.Unlock()
 
 	if err := devices.removeMetadata(info); err != nil {
-		devices.devicesLock.Lock()
-		devices.Devices[info.Hash] = info
-		devices.devicesLock.Unlock()
 		log.Debugf("Error removing meta data: %s", err)
 		return err
 	}