core: Drop support for BOARD_PREBUILT_PVMFWIMAGE

Remove the variable as it was only used when the prebuilt was
device-specific but pvmfw is now part of AOSP.

Bug: 237371962
Test: m $(realpath --relative-to=. $ANDROID_PRODUCT_OUT/pvmfw.img)
Change-Id: I5b4c1ffd563e3dccf22ee485cb12866355f5bfe0
diff --git a/core/config.mk b/core/config.mk
index 51e140d..01f06f3 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -165,6 +165,7 @@
 $(KATI_obsolete_var PRODUCT_SUPPORTS_VERITY_FEC,VB 1.0 and related variables are no longer supported)
 $(KATI_obsolete_var PRODUCT_SUPPORTS_BOOT_SIGNER,VB 1.0 and related variables are no longer supported)
 $(KATI_obsolete_var PRODUCT_VERITY_SIGNING_KEY,VB 1.0 and related variables are no longer supported)
+$(KATI_obsolete_var BOARD_PREBUILT_PVMFWIMAGE,pvmfw.bin is now built in AOSP and custom versions are no longer supported)
 # Used to force goals to build.  Only use for conditionally defined goals.
 .PHONY: FORCE
 FORCE: