libroot: generate a name for nameless volumes

Generate a name indicating the volume size and filesystem.

Remove code that was doing that or similar things in various
filesystems.

Change-Id: I6b993735e58cdfaf1f19af575e918614c7fe5679
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5381
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Jessica Hamilton <jessica.l.hamilton@gmail.com>
Reviewed-by: John Scipione <jscipione@gmail.com>