This is workaround to a regression introduced by 48107579abadbe857c8299c38d2ca0a3f8f354c8. With current
"lib/texinfo.tex", 'texi2dvi' is not able to produce a valid output
for a Texinfo document containing a @synindex command. As a
consequence the test "t/txinfo-no-clutter.sh" was failing.
* t/txinfo-no-clutter.sh: Remove use of @synindex command.