test: remove invalid XML

"<!DOCTYPE PUBLIC" must have system literal.

Author: kou

test/test_doctype.rb

@@ -16,12 +16,6 @@ def setup
       @doc_type_system = REXML::Document.new(xml_system).doctype
 
       @pubid = "TEST_ID"
-      xml_public = <<-XML
-      <!DOCTYPE root PUBLIC "#{@pubid}">
-      <root/>
-      XML
-      @doc_type_public = REXML::Document.new(xml_public).doctype
-
       xml_public_system = <<-XML
       <!DOCTYPE root PUBLIC "#{@pubid}" "#{@sysid}">
       <root/>
@@ -33,11 +27,9 @@ def test_public
       assert_equal([
                      nil,
                      @pubid,
-                     @pubid,
                    ],
                    [
                      @doc_type_system.public,
-                     @doc_type_public.public,
                      @doc_type_public_system.public,
                    ])
     end
@@ -56,12 +48,10 @@ def test_to_s_apostrophe
     def test_system
       assert_equal([
                      @sysid,
-                     nil,
                      @sysid,
                    ],
                    [
                      @doc_type_system.system,
-                     @doc_type_public.system,
                      @doc_type_public_system.system,
                    ])
     end