sim: drop use of bfd/configure.host

sim: drop use of bfd/configure.host

These settings might have made sense in darker compiler times, but I
think they're largely obsolete now.  Looking through the values that
get used in HDEFINES, it's quite limited, and configure itself should
handle them.  If we still need something, we can leverage standard
autoconf macros instead, after we get a clear user report.

TDEFINES was never set anywhere and was always empty, so prune that.