Simplify ExpandScalar, Close #4704

See test_expand_scalar_nested_inner_undefined for details
Redmine#4761: remove unused code
Redmine#4761: acceptance test for cf-promises -T
Redmine#4761: rename ReadTimestampFromPolicyValidatedMasterfiles to ReadTimestampFromPolicyValidatedFile
Redmine#4761: GetPromisesValidatedFile() should use GetInputDir() if not hub
Redmine#4761: Add masterdir+inputdir tagging tests.  Simplify and remove dead code.