Documentation: remove unneeded argument in cat-texi.perl

The newly-added use of the warnings pragma exposes that the $menu[0]
argument to printf has long been silently ignored, since there is no
format specifier for it. It doesn't appear that the argument is
actually needed, either: there is no reason to insert the name of one
particular documentation page anywhere in the header that's being
generated.

Remove the unused argument, and since the format specification
functionality is no longer needed, convert the printf to a simple print.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>