docs: Removed section on overlaying action bar
docs: Removed section on overlaying action bar

When we replaced the action bar docs with the new app bar docs,
we chose not to document the deprecated "overlaying the action bar"
functionality. Removing a separate training section that relies on
the now-removed material.

bug: 26502436
Change-Id: I0fe3715a39d5591be6eecbacbd7f68134ecc9f96

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base