Show the app shelf depending on the platform feature

This CL uses PackageManager.
FEATURE_FREEFORM_WINDOW_MANAGEMENT to determine
whether app shelf should be displayed, and removes
config_enableAppShelf flag that was previously used for that.

Bug: 25329519
Change-Id: I6460eca8e158b0e114e8f2cfdfea4a2e5eadd03b
2 files changed