Access PRODUCT_ variables directly

This CL simplifies the PRODUCTS.$(INTERNAL_PRODUCT).X accesses of
product variables, and removes unnecessary stripping of them.

Replace: '\$\(PRODUCTS\.\$\(INTERNAL_PRODUCT\)\.([^\)]*)\)' with '$(\1)'
Replace: '\$\(strip\s*\$\(PRODUCT_([^\)]*)\)\)' with '$(PRODUCT_\1)'

A few minor manual tweaks.

Bug: 116769560
Test: presubmit
Change-Id: I70c54f1582e3cc780028535960147d99ebc2e0e1
diff --git a/core/app_certificate_validate.mk b/core/app_certificate_validate.mk
index 6d3fdc8..c01526a 100644
--- a/core/app_certificate_validate.mk
+++ b/core/app_certificate_validate.mk
@@ -2,9 +2,9 @@
 ifeq (true,$(non_system_module))
   ifneq (,$(filter $(dir $(DEFAULT_SYSTEM_DEV_CERTIFICATE))%,$(LOCAL_CERTIFICATE)))
     CERTIFICATE_VIOLATION_MODULES += $(LOCAL_MODULE)
-    ifeq (true,$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_ENFORCE_ARTIFACT_SYSTEM_CERTIFICATE_REQUIREMENT))
-      $(if $(filter $(LOCAL_MODULE),$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_ARTIFACT_SYSTEM_CERTIFICATE_REQUIREMENT_WHITELIST)),,\
+    ifeq (true,$(PRODUCT_ENFORCE_ARTIFACT_SYSTEM_CERTIFICATE_REQUIREMENT))
+      $(if $(filter $(LOCAL_MODULE),$(PRODUCT_ARTIFACT_SYSTEM_CERTIFICATE_REQUIREMENT_WHITELIST)),,\
         $(call pretty-error,The module in product partition cannot be signed with certificate in system.))
     endif
   endif
-endif
\ No newline at end of file
+endif