Do not override next keyguard when entering edit mode

This change removes the override of the next keyguard to GONE, and rely
on keyguard signals to determine that. This avoids a rare issue where
the override doesn't get properly cleared and it ends up in GONE state
(empty lockscreen) when leaving the hub.

Test: manual
Fix: 441276968
Flag: EXEMPT BUGFIX
Change-Id: Ie94761586057ce7229d87348b92baf5e3bd4b375