btif: Don't persist remote devices to the config

We don't need to persist the unpaired devices to NVRAM
so skip saving them.

This fixes a regression in a previous patch where the most recent
instead of the least recent devices would be removed, making some
devices unpairable in extremely busy environments.

This is a backport of http://r.android.com/210955 and
http://r.android.com/212838 together.

Bug: 26071376

Change-Id: If7ee9d960f70c836bf08b78da5f3fc852ba60a85