PhoneAccountRegistrar#getSimCallManager should consider disabled PhoneAccounts.

The enabled property of a PhoneAccount doesn't apply to connection managers.
This change simply iterates over all phone accounts, even if they're disabled,
to find the active call manager.

Without this change, the default call manager would be set to "None" in the
Dialer UI. getSimCallManager would return null because the default call
manager's PhoneAccount is disabled.

Bug: 21520812
Change-Id: Ieae8f5c377c47111acf262ff4bc0cf07db6ef64d