scripts: Remove unused :signal_h from POSIX imports

scripts/dpkg-distaddfile.pl

@@ -22,7 +22,7 @@ use strict;
 use warnings;
 
 use POSIX;
-use POSIX qw(:errno_h :signal_h);
+use POSIX qw(:errno_h);
 use Dpkg;
 use Dpkg::Gettext;
 use Dpkg::ErrorHandling;

scripts/dpkg-genchanges.pl

@@ -23,7 +23,7 @@ use strict;
 use warnings;
 
 use Encode;
-use POSIX qw(:errno_h :signal_h);
+use POSIX qw(:errno_h);
 use Dpkg;
 use Dpkg::Gettext;
 use Dpkg::Checksums;

scripts/dpkg-shlibdeps.pl

@@ -24,7 +24,7 @@
 use strict;
 use warnings;
 
-use POSIX qw(:errno_h :signal_h);
+use POSIX qw(:errno_h);
 use Cwd qw(realpath);
 use File::Basename qw(dirname);