Fix Taskbar Container not being aligned center in 3 button nav mode

We were applying padding to taskbar container in 3 button navigation mode which we don't need as icon size are already correct.

Test: Manual, Presubmit
Bug: 364492586
Flag: EXEMPT bugfix
Change-Id: Ib9bf55edf2b7bb67fcbeb044e0ad1e90027b17a6