classes/sanity: remove texi2html from required host utilities
texi2html is not actually required to build world of OE-Core anymore,
so we don't need to mandate it. The only difference without it (verified
with buildhistory) is that groff doesn't produce HTML documentation; the
rest of its docs are still produced and packaged and no other packages
are affected.
Part of the work towards [YOCTO #2423].
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
