erofs: avoid duplicated permission check for "trusted." xattrs

Don't recheck it since xattr_permission() already
checks CAP_SYS_ADMIN capability.

Just follow 5d3ce4f701 ("f2fs: avoid duplicated permission check for "trusted." xattrs")

Reported-by: Hongyu Jin <hongyu.jin@unisoc.com>
[ Gao Xiang: since it could cause some complex Android overlay
  permission issue as well on android-5.4+, it'd be better to
  backport to 5.4+ rather than pure cleanup on mainline. ]
Cc: <stable@vger.kernel.org> # 5.4+
Link: https://lore.kernel.org/r/20200811070020.6339-1-hsiangkao@redhat.com
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

fs/erofs/xattr.c

@@ -473,8 +473,6 @@ static int erofs_xattr_generic_get(const struct xattr_handler *handler,
 			return -EOPNOTSUPP;
 		break;
 	case EROFS_XATTR_INDEX_TRUSTED:
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
 		break;
 	case EROFS_XATTR_INDEX_SECURITY:
 		break;