Correct string ConfirmDeviceCredentialActivity

* If there is a managed profile but a separate
  profile challenge is not enabled, use the device
  title and subtitle in ConfirmDeviceCredentialActivity.

Manual testing
* Set device PIN
* Create a work profile using TestDPC
* adb shell am start --user 10 -a android.app.action.CONFIRM_DEVICE_CREDENTIAL
* Verify title says 'Enter your device...'
* Add a work profile PIN
* adb shell am start --user 10 -a android.app.action.CONFIRM_DEVICE_CREDENTIAL
* Verify title says 'Enter your work...'
* Do the same for pattern and password

Bug: 163108636
Test: manual testing
Change-Id: I8b61e7d2df5792cbdb2e12b19e5a5582ea2290b7