buildhistory: Simplify intercept call sites and drop SSTATEPOSTINSTFUNC usage

buildhistory: Simplify intercept call sites and drop SSTATEPOSTINSTFUNC usage

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.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>