rbd: remove no longer used rados_cmd helper

all librados interaction is now via our XS binding, the last usage was
removed in 41aacc6cde

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
Reviewed-By: Aaron Lauterer <a.lauterer@proxmox.com>
Tested-By: Aaron Lauterer <a.lauterer@proxmox.com>

src/PVE/Storage/RBDPlugin.pm

@@ -124,12 +124,6 @@ my $rbd_cmd = sub {
     return $build_cmd->('/usr/bin/rbd', $scfg, $storeid, $op, @options);
 };
 
-my $rados_cmd = sub {
-    my ($scfg, $storeid, $op, @options) = @_;
-
-    return $build_cmd->('/usr/bin/rados', $scfg, $storeid, $op, @options);
-};
-
 # needed for volumes created using ceph jewel (or higher)
 my $krbd_feature_update = sub {
     my ($scfg, $storeid, $name) = @_;