Only use readline/history.h if no edit/readline/redline.h

it seems edit/readline/readline.h and readline/history.h are
incompatible on FreeBSD, so only include one.  Hopefully this works on
OpenBSD still.

bin/varnishadm/varnishadm.c

@@ -38,12 +38,12 @@
 #    include <edit/readline/readline.h>
 #  elif HAVE_READLINE_READLINE_H
 #    include <readline/readline.h>
+#    ifdef HAVE_READLINE_HISTORY_H
+#      include <readline/history.h>
+#    endif
 #  else
 #    include <editline/readline.h>
 #  endif
-#  ifdef HAVE_READLINE_HISTORY_H
-#    include <readline/history.h>
-#  endif
 #endif
 
 #include <errno.h>