Fix spot not disappear in some case

Bug: When a pointer device exist and it not has event,turn on the show touches in settings, use finger press screen not leave, use command "adb shell settings put system show_touches 0" to turn off show touches, the spot will stay on screen.

Fix Method: call clearSpots method in PointerController when show touches turn off.

Signed-off-by: lilinnan <lilinnan@xiaomi.corp-partner.google.com>
Change-Id: I085b6aeb43771607b4265384f76e17d48beff00c