[O] Old style backquotes in ox-texinfo.el

[James Harkins]

Incidentally, while I was trying different versions last night (for the 
LaTeX starred-figure issue), I saw the following warnings during "make":

In toplevel form:
ox-texinfo.el:1683:1:Warning: !! The file uses old-style backquotes !!
This functionality has been obsolete for more than 10 years already
and will be removed soon.  See (elisp)Backquote in the manual.
ox-texinfo.el:1717:1:Warning: !! The file uses old-style backquotes !!
This functionality has been obsolete for more than 10 years already
and will be removed soon.  See (elisp)Backquote in the manual.

I don't see that this is logged at http://orgmode.org/worg/org-issues.html 
-- while it's not a critical issue obviously, it seems untidy and I'm at 
pains to imagine a good reason to retain syntax that has been deprecated 
for such a long time.

hjh