Add PRODUCT_BOOT_JARS to derive BOOTCLASSPATH

- BOOTCLASSPATH now is product-configurable;
- No need to maintain the duplicate values in core/dex_preopt.mk.
- clean up some legacy ALL_PREBUILTs.
Bug: 9990214

Change-Id: Ie3953e66d282e335bb7782b0ebd56102c35ec10e
diff --git a/core/product.mk b/core/product.mk
index 89bce1d..35b5b84 100644
--- a/core/product.mk
+++ b/core/product.mk
@@ -96,7 +96,8 @@
     PRODUCT_VENDOR_KERNEL_HEADERS \
     PRODUCT_FACTORY_RAMDISK_MODULES \
     PRODUCT_FACTORY_BUNDLE_MODULES \
-    PRODUCT_RUNTIMES
+    PRODUCT_RUNTIMES \
+    PRODUCT_BOOT_JARS
 
 
 define dump-product
@@ -208,6 +209,7 @@
 
 
 _product_stash_var_list := $(_product_var_list) \
+	PRODUCT_BOOTCLASSPATH \
 	TARGET_ARCH \
 	TARGET_ARCH_VARIANT \
 	TARGET_CPU_VARIANT \