Revert "net: don't clear all errors on close"

You're supposed to clear the error queue before any I/O operations. Per
SSL_get_error(3) man page.

This reverts commit ee3ed37300.

lib/pure/net.nim

@@ -1006,6 +1006,7 @@ proc close*(socket: Socket) =
   try:
     when defineSsl:
       if socket.isSsl and socket.sslHandle != nil:
+        ErrClearError()
         # Don't call SSL_shutdown if the connection has not been fully
         # established, see:
         # https://github.com/openssl/openssl/issues/710#issuecomment-253897666