sim: delete old breakpoint code

sim: delete old breakpoint code

This code relies on the old sim-break module, but that was deleted in 2003.
The module only existed for gdb to tell the sim to set breakpoints on its
behalf, but then that logic was abandoned in favor of gdb knowing all about
proper breakpoints (since it does already for non-sim targets).  Some dead
code lived on in the older ports though -- clean it up now.