Remove enabled flag insets_decoupled_configuration

The mDecorTypes and mConfigTypes are always 0, so the related
logic becomes no-op.

Also remove allows_screen_size_decoupled_from_status_bar_and_cutout
because it is ignored if insets_decoupled_configuration is true.

Bug: 409608996
Bug: 409609590
Flag: EXEMPT flag removal
Test: DisplayPolicyTests
Change-Id: Ibdaa3e18be93cb1ebe8b3bf0589bbf8424f78e96