Make RELEASE_PLATFORM_VERSION a release config flag to set platform version.

Bug: 282838389
Test: Treehugger
Change-Id: Ic6dacbdee7d2408aa8b25b4df59bf9bbc566d747
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 4d1e3df..69e7051 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -40,8 +40,7 @@
   include $(INTERNAL_BUILD_ID_MAKEFILE)
 endif
 
-DEFAULT_PLATFORM_VERSION := VP1A
-.KATI_READONLY := DEFAULT_PLATFORM_VERSION
+# Set release configuration. The default resides in build/release/build_flags.mk.
 MIN_PLATFORM_VERSION := UP1A
 MAX_PLATFORM_VERSION := VP1A