Remove the custom X509v3 extensions stack

Remove the custom X509v3 extensions stack

This is essentially unused. The only consumer, www/kore,-acme is in the
process of being fixed. It is also incomplete: in particular, the verifier
doesn't learn about extensions added to the list, making the entire
exercise rather pointless. So let's ditch that crap.

This was the last consumer of the horror that is OBJ_bsearch_().
The even worse OBJ_bsearch_ex_() is still being "used" by M2Crypto...

This prepares the removal of X509V3_EXT_{add{,_list,_alias},cleanup}().
and removes another piece of thread-unsafe global state.

ok jsing