eliminate sv_compile_2op, sv_compile_2op_is_broken

eliminate sv_compile_2op, sv_compile_2op_is_broken

These two functions, which have been a pimple on the face of perl for
far too long, are no longer needed, now that regex code blocks are
compiled in a sensible manner.

This also allows S_doeval() to be simplified, now that it is no longer
called from sv_compile_2op_is_broken().