enforcePhoneAccounts should unregister unresolvable accts

Accounts that cannot be resolved anymore should be unregistered to avoid
keeping the unusable account in memory.

Fixes: 281061708
Test: 1 new unit test + manual:
	(1) flash apk that registers accts on diff CS's
        (2) register MAX accts and disable CS
        (3) app should repeat step 2 mutliple times
        expect: accts unregistered after disabling CS and
                registering another acct

Change-Id: Iddd205d4e9c4013fdd6baaeb78e7b299410d2327