cpu/amd/microcode: Remove dead Makefile

Change-Id: If9d1e28ac50b8ca227b2c09dbbfdd3c9b60aca6a
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47718
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/cpu/amd/microcode/Makefile.inc

@@ -1,2 +0,0 @@
-ramstage-y += microcode.c
-romstage-y += microcode.c