Don't bind outgoing TCP sockets anymore.

The code introduced in commit 41a05f59ba2c3eb5caab555f096ed1b9fbe69ee3 is not
needed anymore, since tinc has been able to handle UDP packets from a different
source address than those of the TCP packets since 1.0.10.  When using multiple
BindToAddress statements, this code does not make sense anymore, we do want the
kernel to choose the source address on its own.