pg_standby: Don't use HAVE_WORKING_LINK

HAVE_WORKING_LINK is meant to indicate support for hard links, mainly
for Windows.  Here it is used for soft links on Unix, and the
functionality is optional anyway, so we can just make it error out
normally if needed.

Discussion: https://www.postgresql.org/message-id/flat/72fff73f-dc9c-4ef4-83e8-d2e60c98df48%402ndquadrant.com

contrib/pg_standby/pg_standby.c

@@ -144,10 +144,8 @@ CustomizableInitialize(void)
 	switch (restoreCommandType)
 	{
 		case RESTORE_COMMAND_LINK:
-#ifdef HAVE_WORKING_LINK
 			SET_RESTORE_COMMAND("ln -s -f", WALFilePath, xlogFilePath);
 			break;
-#endif
 		case RESTORE_COMMAND_COPY:
 		default:
 			SET_RESTORE_COMMAND("cp", WALFilePath, xlogFilePath);