Removes libsodim dependency from tests

[djelenc]

Problem: Since libsodium/master defaulted to tweetnacl for CURVE, the use of libsodium became optional. However, Makefile of this project still links to libsodium, which breaks the build of this bindings on a machine that does not have libsodium installed.

(Moreover, it appears that the link was redundant, since building libzmq with libsodium still succeeds.)

[benjamg]

Is this a timing issue in one of the tests? I don't see how this change could have caused the failure otherwise

[xaqq]

unknown location(0): fatal error in "set_socket_options_tcp_only": std::runtime_error: Address already in use

I think it's indeed a timing issue.

[djelenc]

The tests seem to be pretty sporadic: In my case, two of them failed, but when I rerun them, they both passed. However, I'm not sure this "patch" causes that, since it only concerns compiling...