Fix inconsistency in reporting device admin active state.

When a device admin goes away due to a package change, only one of two lists
was being updated, causing an inconsistency in the query for active admins
depending on which API was being called.

This makes sure that mAdminMap stays in sync with mAdminList so that
isActiveAdmin() and getActiveAdmins() returns the same results.

Bug: 11588094
Change-Id: I232608738249492d9fca7e4d7aa7566d96fccf46