Don't unlink an existing socket before binding.

Sockets are normally cleaned up by the X server. Running the server as root

makes the unlink operation always succeed, as well as the subsequent socket

binding (creation in the file system). But success in binding a new socket is

used to detect in-use displays when using -displayfd. So, when running as root,

:0 is never detected as been used and its socket is systematically crushed,

rendering the existing :0 session stale.

--- Xtranssock.c	2019-03-16 22:30:31.000000000 +0100

+++ Xtranssock.c	2021-02-04 16:30:09.853117000 +0100

@@ -1004,8 +1004,6 @@

 	sockname.sun_path[0] = '\0';

 	namelen = offsetof(struct sockaddr_un, sun_path) + 1 + strlen(&sockname.sun_path[1]);

     }

-    else

-	unlink (sockname.sun_path);

     if ((status = TRANS(SocketCreateListener) (ciptr,

 	(struct sockaddr *) &sockname, namelen, flags)) < 0)