Remove obsolete CI workflow files

Author: nanego

.github/workflows/5_1_9.yml

@@ -9,7 +9,7 @@ def assert_checksum(expected, filename)
 
   it "checks core file application_helper checksums" do
     # several methods are overridden and should be reviewed if the checksum change
-    # version 6.0.6 is OK
+    # version 6.0.7 is OK
     assert_checksum %w"64ef301df3413f4a35cbfeb9c9dddeaa", "app/helpers/application_helper.rb"
   end
 end