Dpkg::Deps: Make %relation_ordering package variable private

This variable was not documented, so not part of the public API, neither
used by any other part of the perl scripts.

Addresses Variables::ProhibitPackageVars.

Warned-by: perlcritic

scripts/Dpkg/Deps.pm

@@ -278,7 +278,7 @@ This function is mainly used to implement the sort() method.
 
 =cut
 
-our %relation_ordering = (
+my %relation_ordering = (
 	undef => 0,
 	REL_GE() => 1,
 	REL_GT() => 2,