/usr/share/mercurial/templates/paper/filelogentry.tmpl is in mercurial-common 2.8.2-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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<td class="age">{date|rfc822date}</td>
<td class="author">{author|person}</td>
<td class="description"><a href="{url|urlescape}rev/{node|short}{sessionvars%urlparameter}">{desc|strip|firstline|escape|nonempty}</a>{inbranch%changelogbranchname}{branches%changelogbranchhead}{tags%changelogtag}{rename%filelogrename}</td>
</tr>
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