Revert "Switch Conscrypt to EC_GROUP_new_arbitrary."

This reverts commit f695b9fa2d3b67f95cc40fb485db5ee73da60f25. Having a
different API for this case than upstream is more trouble than is worth it.  A
separate "incomplete EC_GROUP" state is a nuisance, but not much more of a
nuisance for future hopes than having separate "static EC_GROUP" and "arbitrary
EC_GROUP" buckets.

(BoringSSL will keep both APIs around until this is cycled everywhere so we
won't need more multi-sided changes.)

Change-Id: Iad4604a04d75b29b9aac9dfde0f9ae18964017e8
1 file changed