Stop setting Settings.Global.REQUIRE_PASSWORD_TO_DECRYPT

This setting was specific to FDE, so it no longer serves any purpose.
Both the Settings app and LockSettingsService can potentially set it,
but only to the value 0.  This CL removes the corresponding code from
LockSettingsService, so this setting will no longer be set.

Test: atest com.android.server.locksettings
Bug: 208476087
Change-Id: I34b749ac0aeb7f38d8208b10f29d3b061aadc40c