util-date: cleanup to use %X instead of manually determining user's time
The code have been asking config whether the user has 12 or 24 time format, and then used that for prints. As far as I can see config gets the value from environment.
In addition, there was a bug: LOCALE_DEFAULT time format used "%l:%M %P" which is always AM/PM, even though the comment said that the time should be locale default here.
Let's remove all that complexity, and use the %X specifier directly which gives time in a locale preferred format.