[Halld-offline] Use the dc-2 tags, please

[Mark Ito]

Folks,

I've decided that for the data challenge versions, we are better off 
using tags and not the branch. I think the idea of tags is more 
transparent and using tags-only only costs me one very tiny step each 
time we update the software. Using the branch turned out to be a false 
economy for yours truly.

The current versions of the code are

   tags/sim-recon-dc-2.4
   tags/hdds-dc-2.1

and reflect the recommended versions at the end of the day on Friday. 
People are henceforth encouraged _not_ to use the branch.

I've update the conditions page at

https://halldweb1.jlab.org/data_challenge/02/conditions/data_challenge_2.html

to reflect this change.

   -- Mark

-- 
Mark M. Ito, Jefferson Lab, marki at jlab.org, (757)269-5295