Fix Debian copyright test expected output aboutcode-org#2777

This removes the public domain license that was previously one of the
expected outputs of the Debian Slim Copyright license detection test.
The public domain license is not an actual license for this GNU tar
file.

Signed-off-by: Kevin Ji <kyji1011@gmail.com>

tests/packagedcode/data/debian/copyright/debian-slim-2021-04-07/usr/share/doc/tar/copyright-detailed.expected.yml

@@ -1,26 +1,10 @@
 primary_license:
 declared_license:
-license_expression: public-domain AND gpl-3.0-plus AND gpl-2.0-plus
+license_expression: gpl-3.0-plus AND gpl-2.0-plus
 copyright: |
   Copyright (c) 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1999, 2000, 2001, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
   Copyright (c) 2006, 2007 Bdale Garbee <bdale@gag.com>
 matches:
-  - score: '70.0'
-    start_line: 2
-    end_line: 2
-    matcher: 2-aho
-    rule_length: 2
-    matched_length: 2
-    match_coverage: '100.0'
-    rule_relevance: 70
-    identifier: public-domain_bare_words.RULE
-    license_expression: public-domain
-    is_license_text: no
-    is_license_notice: no
-    is_license_reference: yes
-    is_license_tag: no
-    is_license_intro: no
-    matched_text: public domain
   - score: '100.0'
     start_line: 20
     end_line: 26