Refactor 'in_make' to mean Kati is not skipped.

In Nougat and before, Make wrote a marker file to indicate that
soong_build was invoked from Make to change certain behaviors of Soong
at build time.
https://cs.android.com/android/platform/superproject/+/android-7.1.2_r36:build/core/soong.mk;l=70-73;drc=ae18638b0406ad107b0882a02a13cdd8b92f2a4e

Things have changed, and now soong_build is invoked from soong_ui, which
supports a --skip-make configuration flag:
https://cs.android.com/android/platform/superproject/+/master:build/soong/ui/build/build.go;l=31-33;drc=680387bf1d3ce7cbc77f535be7c42cec411b1687

Thus, the various remnants of 'EmbeddedInMake' and 'inMake'
configuration are misleading, since soong_build is no longer invoked
from Make. This CL refactors all instances to actually mean that
Kati is enabled (not skipped with --skip-make), and will run after
soong_build finishes, so Kati-specific behavior like the AndroidMk
singleton should run.

Test: TH presubmit

Change-Id: I576ab8e54f99f5c8ddf9feaf9a828019b279e266

scripts/build-aml-prebuilts.sh

@@ -12,7 +12,7 @@
 
 export OUT_DIR=${OUT_DIR:-out}
 
-if [ -e ${OUT_DIR}/soong/.soong.in_make ]; then
+if [ -e ${OUT_DIR}/soong/.soong.kati_enabled ]; then
   # If ${OUT_DIR} has been created without --skip-make, Soong will create an
   # ${OUT_DIR}/soong/build.ninja that leaves out many targets which are
   # expected to be supplied by the .mk files, and that might cause errors in
@@ -32,8 +32,8 @@ source build/envsetup.sh
 
 my_get_build_var() {
   # get_build_var will run Soong in normal in-make mode where it creates
-  # .soong.in_make. That would clobber our real out directory, so we need to
-  # run it in a different one.
+  # .soong.kati_enabled. That would clobber our real out directory, so we need
+  # to run it in a different one.
   OUT_DIR=${OUT_DIR}/get_build_var get_build_var "$@"
 }