scripts/package-metadata.pl: remove broken detection of self-dependencies
A self-dependency is not an error worth a warning; rather, it is very
common: whenever there are dependencies between different binary packages
originating from the same source package, such dependencies occur. Not
actually generating dependency rules is correct, but already handled a few
lines below.
A typo prevented this redundant rule from working, which is the reason the
warning was not actually printed.
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>