This package is needed for proper handling of image filenames
containing periods (in addition to the period before the
extension).
Unfortunately, grffile breaks in the latest texlive update.
Until a fix is released (see ho-tex/oberdiek#73) it seems best
to remove this from the default template.
This may cause problems if you have filenames with periods.
The workaround is to put `\usepackage{grffile}` in header-includes,
and be sure you're using an older version of texlive packages.
See #5848. We will leave that issue open to remind us to
check upstream, and restore grffile when it's possible to
do so.
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