Remove dead code and doc regarding the old SocksSocket option
In `entry_connection_t`, there is still `is_socks_socket` option that is simply not used. Other place is this log which should be renamed to mention "Unix socket". ``` log_info(LD_NET, "Closing SOCKS SocksSocket connection"); ``` Finally, the man page is still listing the option within another option (although `SocksSocketsGroupWritable` is still a thing that we should probably rename). ``` SocksSocketsGroupWritable 0|1 If this option is set to 0, don’t allow the filesystem group to read and write unix sockets (e.g. SocksSocket). If the option is set to 1, make the SocksSocket socket readable and writable by the default GID. (Default: 0) ```
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