Don't export deprecated TcpSocket, IpAddr

[mlubin]

These weren't exported in 0.3

CC @sbromberger @jakebolewski

[sbromberger]

It seems strange to me that UdpSocket was exported, especially since it only appears in base/socket.jl. @Keno - is there a reason it should follow different behavior than its related classes?

[mlubin]

Both UDPSocket and TCPSocket are now exported in 0.4, so not sure if there's an issue here.

[sbromberger]

The result of this patch would bring 0.4 inline with 0.3 with respect to the export of UdpSocket, but I don't know why this (inconsistent) behavior exists in 0.3. Would it be better to file a PR against 0.3 making TcpSocket and IpAddr consistent with UdpSocket (likely by exporting them, so things don't break) first? Then, whatever we decide to do in 0.4 is consistent across all three types.

ETA: UdpSocket was added to exports via #5697

[mlubin]

Can't comment on the utility of exporting since I'm not familiar with the code, but asking for changes in 0.3 will delay the resolution of this.

[mlubin]

Another question is why deprecations are needed at all for names that weren't exported. It seems like the convention now is to make the old names available through Compat if needed.