Remove unused critical accessibility settings from backup/restore

ACCESSIBILITY_SPEAK_PASSWORD was deprecated in O and is forced true with
a default.

UI_NIGHT_MODE was removed from being backed up since M.

This is to clean up the critical accessibility settings check.

Bug: 78227065
Test: 1) atest SettingsBackupTest
2) atest SettingsValidatorsTest
3) manual: d2d does not restore ACCESSIBILITY_SPEAK_PASSWORD or
UI_NIGHT_MODE

Change-Id: I50478fc8a476817301cce7187165a79b249ee31a