We planned to drop SSTATEPOSTINSTFUNC some time ago with the introduction of
postfuncs. Finally get around to doing that which should make the buildhistory
code a little more readable.

Unfortunately ordering the buildhistory function calls after the sstate ones is
difficult without coding that into the sstate class. This patch does that to
ensure everything functions as expected until we can find a better way. This is
still likely preferable than the generic sstate postfuncs support since the function
flow is much more readable.

(From OE-Core rev: 78ca086441b21dedd9c471a3d3200c24fd9ec8d2)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit c9e2a8fa2f0305ef1247ec405555612326f798f8)
Signed-off-by: Steve Sakoman <steve@sakoman.com>