Revert 218616 "[net/dns] Perform A/AAAA queries for AF_UNSPEC re..."

Revert 218616 "[net/dns] Perform A/AAAA queries for AF_UNSPEC re..."

This was causing crashes in the case of DNS responses with no addresses.

> [net/dns] Perform A/AAAA queries for AF_UNSPEC resolutions in parallel. 
> 
> The second DnsTransaction is scheduled as a second job on the resolver's
> PrioritizedDispatcher, at the beginning of its priority queue.  The two
> DnsTransactions run independently of each other, although if one of them
> finishes with an error, the other one will be scrapped immediately, and
> the Job will fall back to ProcTask. 
> 
> BUG=174992
> 
> Review URL: https://chromiumcodereview.appspot.com/19498003

TBR=mmenke@chromium.org
BUG=277625
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=219027

[mmenke, 2013-08-22 16:05:14]

Committed patchset #1 manually as r219027.