build: don't link bison against libreadline
Reported by Paul Smith <psmith@gnu.org>.
https://lists.gnu.org/r/bug-bison/2020-10/msg00001.html

--- a/Makefile.in
+++ b/Makefile.in
@@ -3456,7 +3456,6 @@
   $(LIB_SETLOCALE_NULL)                         \
   $(LIBICONV)                                   \
   $(LIBINTL)                                    \
-  $(LIBREADLINE)                                \
   $(LIBTEXTSTYLE)

 @ENABLE_YACC_TRUE@nodist_bin_SCRIPTS = src/yacc