scripts/t: Delete DEB_VENDOR from the environment to get reliable results

debian/changelog

@@ -72,6 +72,7 @@ dpkg (1.18.2) UNRELEASED; urgency=low
     - Set SIGINT, SIGTERM and SIGPIPE to their default actions to get
       deterministic behavior.
     - Add test cases for the makefile snippets.
+    - Delete DEB_VENDOR from the environment to get reliable results.
   * Packaging:
     - Make the libdpkg-dev package Multi-Arch:same.
     - Mark libio-string-perl as <!nocheck>.

scripts/t/Dpkg_Vendor.t

@@ -18,6 +18,9 @@ use warnings;
 
 use Test::More tests => 6;
 
+# Delete variables that can affect the tests.
+delete $ENV{DEB_VENDOR};
+
 use_ok('Dpkg::Vendor', qw(get_vendor_dir get_current_vendor get_vendor_object));
 
 is(get_vendor_dir(), $ENV{DPKG_ORIGINS_DIR}, 'Check vendor dir');