Remove the PRODUCT-* goal

I've switched all the build server configs to using TARGET_PRODUCT /
TARGET_BUILD_VARIANT and explicit goals instead.

Remove tools/check_builds.sh which relied on this, but hasn't been
touched in a long time.

Test: m PRODUCT-test
Test: treehugger
Change-Id: If5f8c714567b33aeb38223c176ca24ea649eb57d
diff --git a/core/envsetup.mk b/core/envsetup.mk
index 05957cd..3e8fd3f 100644
--- a/core/envsetup.mk
+++ b/core/envsetup.mk
@@ -82,8 +82,6 @@
 
 # ---------------------------------------------------------------
 # The product defaults to generic on hardware
-# NOTE: This will be overridden in product_config.mk if make
-# was invoked with a PRODUCT-xxx-yyy goal.
 ifeq ($(TARGET_PRODUCT),)
 TARGET_PRODUCT := aosp_arm
 endif
@@ -94,6 +92,13 @@
 TARGET_BUILD_VARIANT := eng
 endif
 
+TARGET_BUILD_APPS ?=
+
+.KATI_READONLY := \
+  TARGET_PRODUCT \
+  TARGET_BUILD_VARIANT \
+  TARGET_BUILD_APPS
+
 # ---------------------------------------------------------------
 # Set up configuration for host machine.  We don't do cross-
 # compiles except for arm/mips, so the HOST is whatever we are