use directly makeinfo in texi2dvi instead of working around

[Patrice Dumas]

Hello,

The sed use in texi2dvi, with comment_iftex could be replaced
by a direct use of makeinfo, starting with 5.0, released in 16 February
2013 (as stated in the comment).

The following call would be the best, to avoid having a processing as
Info done:
 makeinfo -c TEXINFO_OUTPUT_FORMAT=plaintexinfo --iftex --no-ifinfo

Can it be done now or does it need to wait some years?  My feeling is
that we do not need to wait, as normally users get texi2dvi together
with makeinfo/texi2any, such that 10 years is more than enough.

-- 
Pat