Prevent using config.mk from make, clean up unused code

Print a large warning and stop unless we're using ckati. Then remove a
bunch of code that soong_ui doesn't use.

Test: command make -f build/core/config.mk
Test: . build/envsetup.sh; lunch aosp_arm-eng; m nothing
Test: cs/CALLED_FROM_SETUP
Change-Id: Ib823d5ef8955fb68dbc9a035cfa8d5ac4903534a