efi-loader: drop harmful assertion

This fixes a bug introduced by 7be4b23649.

The function `efi_loader_get_device_part_uuid()` handles NULL
gracefully, and it is called with NULL in gpt-auto-generator.

Fixes #22862.

src/shared/efi-loader.c

@@ -62,8 +62,6 @@ int efi_loader_get_device_part_uuid(sd_id128_t *ret) {
         _cleanup_free_ char *p = NULL;
         int r, parsed[16];
 
-        assert(ret);
-
         if (!is_efi_boot())
                 return -EOPNOTSUPP;