Remove IPv6 section from dns/arm/general.rst

The following discussion from !3616 (merged) should be addressed:

• @ondrej started a discussion:

  @sgoldlust wrote in a commit message:

  I am not sure the IPv6 Addresses section belongs here; it is general DNS reference information, but it seems like we either need to give a lot more information about other general stuff, or just remove this bit. I also question whether the Internet Drafts and Other Documents About BIND sections are necessary here; Internet Drafts does not have any useful information and Other Documents seems very incomplete.

  I recommend removing the Bibliography heading entirely and just making this entire reference section about the RFCs.