When loading packages affected by a change to a particular path, ignore archived packages

Summary:
Ref T11650. Currently, we load packages and then discard the archived ones.

However, this gets "dominion" rules (where a more-general package gives up ownership if a more-specific package exists) wrong if the more-specific package is archived: we incorrectly give up ownership.

Instead, just ignore these packages completely when loading affected packages. This is slightly simpler.

(There are technically two pieces of code we have to do this for, which should be a single piece of code but which haven't yet been unified.)

Test Plan:

• Created packages:
  • Package A, on "/" (strong dominion, autoreview).
  • Package B, on "/x/" (weak dominion, autoreview).
  • Package C, on "/x/y" (archived, autoreview).
• Create a revision affecting "/x/y".
• Saw correct path ownership in table of contents ("B", strongest package only).
• Saw correct autoreview behavior (A + B).
• (Prior to patch, in master, reproduced the problem behaviors described in T11650, with bad dominion rules and failure to autoreview B.)

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11650

Differential Revision: https://secure.phabricator.com/D16564