The heading is "unlinked" before adding it to the TOC.

```
% pandoc --to=latex
<http://example.com/> {-}
=========================
^D
\section*{\texorpdfstring{\url{http://example.com/}}{http://example.com/}}\label{httpexample.com}
\addcontentsline{toc}{section}{{http://example.com/}}
```
