Don't supply time stamps for Capsa packets for now.

The time stamps aren't known to be right, so don't provide them - that
way, instead of users reading Capsa files and getting the wrong idea
about the time stamps, they'll get no time stamps and have to ask for
our help, at which point we can ask them for *their* help in seeing what
Capsa thinks the time stamps are.  (The joys of reverse-engineering.)

Change-Id: I77e12c09f2bc74b50a1b2b226fa6da3e8c0fedf9
Reviewed-on: https://code.wireshark.org/review/4685
Reviewed-by: Guy Harris <guy@alum.mit.edu>