CRM-16373 - Simplify UpdateConfigBackend and doSiteMove()

CRM-16373 - Simplify UpdateConfigBackend and doSiteMove()

doSiteMove() has been performing a search-and-replace against data
structures which haven't exist since at least 4.0; it seems quite unlikely
that this works.  Anecdotally, the workflow around this either incomplete or
buggy/broken.  Simplifying this is simply a reflection of the reality that
it doesn't do what it was written to do.

Instead, doSiteMove() now resets to a standard baseline/default.