Delete the NetBSD ping6.

From now on the ping6 binary will be the iputils version in
external/ping. That version shares code and behaviour with our
IPv4 ping binary, and will be extended to support permissionless

(cherry-pick of c7b4597ed06f8b87e3805f17a5636642f40a5aa0.)

Bug: 9469682
Change-Id: I10bede90f2f92bb5fff99c159cb2d00036c4df21
4 files changed
tree: 4b825dc642cb6eb9a060e54bf8d69288fbee4904

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