We don't want libidn(2) being detected automagically.
Partially reverting upstream stupidity.

--- whois-5.3.0/Makefile
+++ whois-5.3.0/Makefile
@@ -33,17 +33,9 @@
 DEFS += -DLOCALEDIR=\"$(BASEDIR)$(prefix)/share/locale\"
 endif
 
-# libidn support has been autodetected since 5.2.18
 ifdef HAVE_LIBIDN
-$(error Please fix your build system to stop defining HAVE_LIBIDN!)
-endif
-
-ifeq ($(shell $(PKG_CONFIG) --exists 'libidn2 >= 2.0.3' || echo NO),)
 whois_LDADD += $(shell $(PKG_CONFIG) --libs libidn2)
 DEFS += -DHAVE_LIBIDN2 $(shell $(PKG_CONFIG) --cflags libidn2)
-else ifeq ($(shell $(PKG_CONFIG) --exists 'libidn' || echo NO),)
-whois_LDADD += $(shell $(PKG_CONFIG) --libs libidn)
-DEFS += -DHAVE_LIBIDN $(shell $(PKG_CONFIG) --cflags libidn)
 endif
 
 ifdef HAVE_ICONV