Setup: Move wgRCLinkDays logic from Setup to ChangesListSpecialPage

Setup: Move wgRCLinkDays logic from Setup to ChangesListSpecialPage

This is only needed when viewing SpecialRecentChanges (or a related
page). Move the consuming logic to that class, where it can be
maintained as part of the rest of the code. This also makes it
more testable and makes config easier to work with or load from
elsewhere in the future. Aside from some dynamic default values,
configuration should generally not mutate. If there is some domain-
specific way to consume it, the relevant component should be
responsible for doing so. This also means we defer such logic to
where it is needed, instead of unconditionally for all possible
features that might be used.

Bug: T189966
Change-Id: If17608909711d98ac560b6d64f72ba7913a561a9