Revert "Launcher3: Icon pack support"

Pa already has theme engine so another preference for custom icon pack
is redundant use the one in theme settings instead

This reverts commit 01631322b2a1da34cbda89840407b8c8ab92bd94.

Signed-off-by: cj360 <ayunker551@gmail.com>

Conflicts:
	res/values/custom_strings.xml
	res/xml/preferences.xml
	src/com/android/launcher3/IconCache.java
	src/com/android/launcher3/LauncherPreferences.java
	src/com/android/launcher3/LauncherPreferencesActivity.java
	src/com/android/launcher3/Utilities.java

Change-Id: If733803e93b728c97d73bfe72cbc0fa20d65e215