Don't set initial value for SCREENSAVER_COMPONENTS.

We need to use SCREENSAVER_COMPONENTS==null to indicate that the user
hasn't selected a dream.

Test: atest NudgeToSetupDreamCallbackTest
Test: manually flash device and run
Bug: 213368707
Change-Id: I7140197690d266fbd70cf38cd7a96f175b247a75
1 file changed