safesocket: remove ConnectionStrategy (#10662)

This type seems to be a migration shim for TCP tailscaled sockets
(instead of unix/windows pipes). The `port` field was never set, so it
was effectively used as a string (`path` field).
Remove the whole type and simplify call sites to pass the socket path
directly to `safesocket.Connect`.

Updates #cleanup

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

safesocket/basic_test.go

@@ -57,8 +57,7 @@ func TestBasics(t *testing.T) {
 	}()
 
 	go func() {
-		s := DefaultConnectionStrategy(sock)
-		c, err := Connect(s)
+		c, err := Connect(sock)
 		if err != nil {
 			errs <- err
 			return