The string variable is never initialized or set,
and the only use is if it is not empty.

In 2007, author Oliver Specht 2007-06-12 04:41:16 in
range fe8e4e77
introduced m_sFootnoteFontName in a pair of commits.

The call to SetFootnoteFontname() was removed in 2008
with commit 009e3f48

The SetFootnoteFontName() function was removed as unused in
commit 6ea66657

Since the footnote name is never set, it is always
empty, and thus this code is useless.

Change-Id: I64898ce9fa6673fbef0106054b5aa5a817c145d5
Reviewed-on: https://gerrit.libreoffice.org/38257Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>