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/ninja_config.mk b/core/ninja_config.mk
index 85a7568..e33ebf5 100644
--- a/core/ninja_config.mk
+++ b/core/ninja_config.mk
@@ -7,7 +7,7 @@
 KATI_OUTPUT_PATTERNS := $(OUT_DIR)/build%.ninja $(OUT_DIR)/ninja%.sh
 
 # Modifier goals we don't need to pass to Ninja.
-NINJA_EXCLUDE_GOALS := all PRODUCT-%
+NINJA_EXCLUDE_GOALS := all
 
 # A list of goals which affect parsing of makefiles and we need to pass to Kati.
 PARSE_TIME_MAKE_GOALS := \