ui: storage backup view: Update remove button on protection change
Currently this works in the backup view for containers/VMs, but not in
the storage backup view. Implement that for the latter part too.
Uses the callback functionality of the load() method of the store to
properly update the UI as soon as the loading has finished.
While at it, refactor the same thing in the grid backup view as well,
removing the current hack in the process.
Signed-off-by: Christoph Heiss <c.heiss@proxmox.com>