Revert "Have all targets in build.ninja"

--gen_all_targets seems to be dropping some intermediate targets,
causing problems when kati is passed a goal and then ninja is run with
checkbuild as a goal, for example with:
m -j PRODUCT-aosp_flounder-userdebug checkbuild

This reverts commit 92bbf566.

Change-Id: If34a790028f8da98fcc713e3f7000d06c63dcf80