tests: remove vzdump_notification test

tests: remove vzdump_notification test

With the upcoming changes in how we send notifications, this one
really becomes pretty annoying to keep working. The location where
templates are looked up are defined in the proxmox_notify crate, so
there is no easy way to mock this for testing.
The test itself seemed not super valuable, mainly testing if
the backup logs are shortened if they ware too long - so they are just
removed.

Signed-off-by: Lukas Wagner <l.wagner@proxmox.com>
Tested-by: Max Carrara <m.carrara@proxmox.com>
Reviewed-by: Max Carrara <m.carrara@proxmox.com>