Edit: This has got so far only 1 supporting vote, and according to our policy, the threshold is 4 votes before the moderators can act. Why the lack of support? To me this looks like a no-brainer; the tags are now synonymous (recall that we have now a separate tag for dc.parallel-comp), and currently the more popular tag is the "wrong" one (non-arxiv), so merging would help to clean up the situation.
If you have some specific doubts regarding this proposal, please leave a comment. If you think this is a bad idea, feel free to downvote.
Edit: It seems that we are getting more and more questions with the [distributed-systems] tag and no top-level arxiv tag. By now we have already 8 such questions. And as far as I can tell, all of those questions could be equally well tagged with [dc.distributed-comp]. Hence I am once again editing this in an attempt to attract the missing supporting vote – if this fails, I promise I will stop bothering you with this issue. :)