[build] Remove obsolete explicit object requirements

As of commit b1caa48 ("[crypto] Support SHA-{224,384,512} in X.509
certificates"), the list of supported cryptographic algorithms is
controlled by config/crypto.h.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/hci/commands/image_trust_cmd.c

 REQUIRING_SYMBOL ( image_trust_commands );
 
 /* Drag in objects typically required for signature verification */
-REQUIRE_OBJECT ( rsa );
-REQUIRE_OBJECT ( md5 );
-REQUIRE_OBJECT ( sha1 );
-REQUIRE_OBJECT ( sha256 );
 REQUIRE_OBJECT ( der );