Remove unused method to change icon background color

Since taskbar and launcher hotseat icons are now the same background
color we don't need the method that it used to use to switch between the
two. (This method was only used in that one place)

Fix: 323952706
Test: Turn on themed icons and dark mode. Compare app icons in taskbar
and in hotseat
Flag: N/A

Change-Id: Ie82073fd1173c464f873a55fd23fad0d9b26cba0