[build] Remove more obsolete explicit object requirements

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

src/hci/commands/image_trust_cmd.c

 		.exec = imgverify_exec,
 	},
 };
-
-/* Drag in objects via command list */
-REQUIRING_SYMBOL ( image_trust_commands );
-
-/* Drag in objects typically required for signature verification */
-REQUIRE_OBJECT ( der );