Build failure for footnotes

Footnotes should work in our documentation as described in https://asciidoctor.org/docs/user-manual/#user-footnotes

The following works fine:

````
Internode-communication over the transport protocol in the {es} cluster.footnote:[<>]
````

However when I try to use footnotes in a list, the build fails. For example:

````
* Internode-communication over the transport protocol in the {es} cluster.footnote:[<>]
````
... results in an error like this when I build the Elasticsearch Reference:
````
INFO:build_docs:---err---
INFO:build_docs:/docs_build/resources/asciidoctor/lib/docbook_compat/convert_lists.rb:51:in `block in munge_list_items': Couldn't remove

for Internode-communication over the transport protocol in the Elasticsearch cluster.<sup>[5]</sup> in