Can't disable password on Android 6.0 (EMUI 4.0)
Thanks to xavier_fakerat's comment that mentioned Android Central Forum. You need to do this:


Set up a pattern password with a backup PIN
Double-tap the power button to activate the lock screen
Do wrong patterns 5 times (at least 4 dots touched to be counted as an attempt), then wait for the cooldown
Select backup PIN, enter your PIN and you could select "none"