bootstd: Drop the system bootdev

This was a work-around for the fact that global bootmeths such as EFI
bootmgr and VBE don't use a particular bootdev, or at least select it
themselves so that we don't need to scan all bootdevs when using that
bootmeth.

Drop the system bootdev entirely.

Signed-off-by: Simon Glass <sjg@chromium.org>

boot/bootstd-uclass.c

@@ -145,12 +145,6 @@ int dm_scan_other(bool pre_reloc_only)
 		}
 	}
 
-	/* Create the system bootdev too */
-	ret = device_bind_driver(bootstd, "system_bootdev", "system-bootdev",
-				 &dev);
-	if (ret)
-		return log_msg_ret("sys", ret);
-
 	return 0;
 }