Delete markdownlint-test-default-config.json, allow MD041 to default to true, add missing headings.

test/trailing_spaces_br.md

@@ -1,6 +1,8 @@
+# trailing_spaces_br
+
 This line has a single trailing space {MD009} 
 This line has two trailing spaces and should be allowed  
 This line has three trailing spaces {MD009}   
 This line has four trailing spaces {MD009}    
  
-{MD009:5}
+{MD009:7}