gprofng: update file texinfo.tex?

[Ruud van der Pas]

Hi team,

I ran into an issue when trying to generate a PDF file from the gprofng.texi
Texinfo file.

I’m using Texinfo 6.7, but texi2pdf did not like my use of @subentry, while this
is supported in 6.7.

It took me quite some time to find out that this was caused by the texinfo.tex
file that is currently in subdirectory binutils-gdb/texinfo.

I was using this file to be more self contained, but it is from 2009 (2009-03-28.05).

Switching to the 2021 version (2021-02-20.11) solved the problem.

We could include the 2021 file in the gprofng/doc directory and use it instead, but
I wonder if it might be better to consider updating the current file in binutils-gdb/texinfo
to a more recent version.

Kind regards, Ruud