Gets rid of the conditional keyguard dismissal in full screen user switcher.

This logic existed to differentiate between boot and switch, at the time
when we wanted to show the switcher on user boot. That's not the case any more,
so the logic has become obsolete.

This also resolve the issue with keyguard not being dimissed in the bug below.

Bug: 112142114
Test: multiple boot/switches on mojave
Change-Id: I82b55bd3d00e5ab7249347d19d804b8945c3c9fc