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/arch/riscv/boot.c

@@ -22,7 +22,7 @@ void arch_prog_run(struct prog *prog)
 {
 	void (*doit)(void *) = prog_entry(prog);
 
-	if (ENV_RAMSTAGE && prog_type(prog) == ASSET_PAYLOAD) {
+	if (ENV_RAMSTAGE && prog_type(prog) == PROG_PAYLOAD) {
 		initVirtualMemory();
 		write_csr(mepc, doit);
 		asm volatile("eret");