Resources: Authorized Site duplication

[t4k]

From @lnarizny: https://lists.coral-erm.org/pipermail/coral-user/2019-March/000507.html

In attempting to add some authorized sites in the Access tab of a resource, I'm running into two problems: 1) duplication, and 2) the inability to remove an authorized site.

Steps to Reproduce:

1. Added some entries to the Authorized Sites list (including editing the default Main Site to have a new label) in Resources Admin
2. Went into my test resource record and found that one of the boxes (probably the former default Main Site) was already ticked
3. Ticked some more boxes and saved, only to find that a couple duplicate entries were produced
4. Unticked some boxes and saved, which did not remove any sites from the list and seemed to create a few more duplicates
5. Unticked all the boxes and saved, to no effect. I tried multiple different boxes different times