Remove dead code from KeyguardUpdateMonitor

mLockIconPressed flag is never set to true as the onLockIconPressed
method is never invoked [1].
mIsAutomotive is never used.

[1]:
https://source.corp.google.com/android-internal/frameworks/base/packages/SystemUI/src/com/android/keyguard/KeyguardUpdateMonitor.java?q=%22onLockIconPressed()%22%20p:android-internal

Bug: 238187419
Test: atest KeyguardUpdateMonitorTest passes
Change-Id: Ie349790c86259b4a75d3e9b5005f364de06bc617