Rewrite obj_xref.c

Rewrite obj_xref.c

Instead of having two unreadable tables placed in a header generated by a
janky perl script from an ugly text file, use a single table inlined in
the C file. This table is used to translate between signature algorithm
OIDs and pairs of OIDs of a message digest and a cipher. The table has
fewer than fifty entries and isn't used in a hot path. Using binary search
is overkill. Just do two linear searches, one for each translation. None
of the original code remains apart from the API.

ok jsing