Remove redundant checks that stop updating systemUI when entering dream

Previous in order to get better transition from lock screen to Dream, we skip the updateSystemUiVisibility by checking keyguard and occluded
states. But since the Dream become activity, there will be an opening app transition for DreamActivity, the original check condition should be able to removed now.
Ref: 4c1e3183
Ref: 380ecb81

Bug: 159790735
Test: atest DisplayPolicyTests
Change-Id: I057e9b2f866c1deaaf41f50f75edc00f6849ea86