Remove the navigation camera icon in keyguard if disabled by DPM

The logic here is incorrect: the camera shortcut is/should be accessible
even with a secure lock screen. As a result, a device with the lock
screen camera disabled by DPM and an insecure lock screen would still
display the unfunctional shortcut.

Change-Id: If1d172932c6c2af596c38e623521c992fdf95402