Don't show the Tasbar Pinning edu for 3 button nav users

The taskbar is already pinned for 3 button nav users so seeing the
taskbar pinning edu tooltip is not useful for them.

Flag: ACONFIG com.android.launcher3.enable_taskbar_pinning TRUNKFOOD
Fix: 322449139
Test: Reset taskbar edu in 3 button mode and ensure that pinning edu
doesn't show up

Change-Id: I9a5da0fc74596056f6e6b1827c67584c2c9cf44e