Allows GSI AVB keys on vendor boot even when not building vendor boot.

This allows system-only builds (which disable vendor images) to inherit
from device makefiles that normally place GSI AVB keys on vendor boot.

Bug: 175594737
Test: lunch system-only build, m, observe warning not failure
Change-Id: Ib6c199d0a47b3b3be2143241d83ab586966cfd1e
diff --git a/core/board_config.mk b/core/board_config.mk
index 1a80348..7ee1de4 100644
--- a/core/board_config.mk
+++ b/core/board_config.mk
@@ -777,9 +777,6 @@
   ifeq (true,$(BOARD_MOVE_RECOVERY_RESOURCES_TO_VENDOR_BOOT))
     $(error Should not set BOARD_MOVE_RECOVERY_RESOURCES_TO_VENDOR_BOOT if not building vendor_boot image)
   endif
-  ifeq (true,$(BOARD_MOVE_GSI_AVB_KEYS_TO_VENDOR_BOOT))
-    $(error Should not set BOARD_MOVE_GSI_AVB_KEYS_TO_VENDOR_BOOT if not building vendor_boot image)
-  endif
 endif
 
 # If BOARD_USES_GENERIC_KERNEL_IMAGE is set, BOARD_USES_RECOVERY_AS_BOOT must not be set.