compare_dg_tests.pl: Remove unused variable from read_sum()

Change-Id: Ib16b5a18dce997f4484291158013b36a61c1098b
diff --git a/compare_dg_tests.pl b/compare_dg_tests.pl
index 27d464b..f70554c 100755
--- a/compare_dg_tests.pl
+++ b/compare_dg_tests.pl
@@ -340,7 +340,6 @@
    my ($sum_file) = @_;
    my $res = empty_result();
    my %testcases;
-   my %unsupported;
    $res->{testcases} = \%testcases;
    my $pending_timeout=0;
    my $current_tool="";