Remove verify_boot_signature.

The immediate motivation is to trim away uses of the <openssl/asn1t.h>
header. Per email with samitolvanen@, this verified boot scheme has been
deprecated for a while, and this target isn't actually used anywhere. It
is only a rough example for OEMs. Accordingly, remove it.

Test: mma
Change-Id: Ie3b6d2c3fb0a6873b81a1a048945ef8258521f16
2 files changed