texi: remove workaround for older Texinfo (4.1) * lib/am/texibuild.am: Here, in the rules generating HTML output. We can do so because, since Automake 1.13, we require Texinfo >= 4.9 anyway. Basically a backport of Automake-NG commit '1.12.2-879-ge6caf5e'. Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>