remove machine/metadata.h from sys/opencrypto/crypto.c

The header was added by the recent keybuf feature (r316343)

MODINFOMD_KEYBUF originally resided here, but was moved to linker.h

This change fixes the build on risc-5 which doesn't have a metadata.h

Detected by Jenkins: https://ci.freebsd.org/job/FreeBSD-head-riscv64-build/1167/console

Reported by:	lwhsu

sys/opencrypto/crypto.c

@@ -86,7 +86,6 @@ __FBSDID("$FreeBSD$");
 #if defined(__i386__) || defined(__amd64__) || defined(__aarch64__)
 #include <machine/pcb.h>
 #endif
-#include <machine/metadata.h>
 
 SDT_PROVIDER_DEFINE(opencrypto);