Revert "Include new storage function volume_send."

This reverts commit b76774e57f.

PVE/Storage/Plugin.pm

@@ -697,14 +697,6 @@ sub volume_snapshot {
     return undef;
 }
 
-sub volume_send {
-    my ($class, $scfg, $storeid, $volname, $ip, $snap,
-	$incremental_snap, $verbose, $limit, $target_path) = @_;
-
-    # implement in subclass
-    die "Volume_send is not implemented for $class";
-}
-
 sub volume_rollback_is_possible {
     my ($class, $scfg, $storeid, $volname, $snap) = @_;