plugin: drop explicit unlink

Go's `net` package [will unlink][1] for us, as long as we used Listen &
friends to create the Unix socket.

Go will even skip the unlink when the socket appears to be abstract
(starts with a NUL, represented by an @), though we must be cautious to
only create sockets with an abstract address on platforms that actually
support it -- this caused [several][2] [bugs][3] before.

  [1]: https://pkg.go.dev/net#UnixListener.SetUnlinkOnClose
  [2]: https://github.com/docker/cli/pull/4783
  [3]: https://github.com/docker/cli/pull/4863

Signed-off-by: Bjorn Neergaard <bjorn.neergaard@docker.com>

cli-plugins/socket/socket_abstract.go

@@ -2,19 +2,8 @@
 
 package socket
 
-import (
-	"net"
-)
-
-func listen(socketname string) (*net.UnixListener, error) {
-	// Create an abstract socket -- this socket can be opened by name, but is
-	// not present in the filesystem.
-	return net.ListenUnix("unix", &net.UnixAddr{
-		Name: "@" + socketname,
-		Net:  "unix",
-	})
-}
-
-func unlink(listener *net.UnixListener) {
-	// Do nothing; the socket is not present in the filesystem.
+func socketName(basename string) string {
+	// Address of an abstract socket -- this socket can be opened by name,
+	// but is not present in the filesystem.
+	return "@" + basename
 }