lib: remove assets infrastructure

Now that only CBFS access is supported for finding resources
within the boot media the assets infrastructure can be removed.
Remove it.

BUG=chromium:445938
BRANCH=None
TEST=Built and ran on glados.

Change-Id: I383fd6579280cf9cfe5a18c2851baf74cad004e9
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/12690
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/vendorcode/google/chromeos/vboot2/vboot_loader.c

@@ -98,7 +98,7 @@ static void vboot_prepare(void)
 	} else if (verstage_should_load()) {
 		struct cbfsf file;
 		struct prog verstage =
-			PROG_INIT(ASSET_VERSTAGE,
+			PROG_INIT(PROG_VERSTAGE,
 				CONFIG_CBFS_PREFIX "/verstage");
 
 		printk(BIOS_DEBUG, "VBOOT: Loading verstage.\n");