security/obfsclient: deprecate and set to expire by the end of the year

• It currently does not build and does not support modern OpenSSL API
• None of the protocols it speaks are all that useful at the present time
• All the newer protocols it could be using either have severe design- level issues, would require way too many external dependencies, or both
• Upstream maintainer lacks motivation, spare cycles, or funding to work on this sort of thing these days