libsecp256k1 no longer has --with-bignum= configure option

configure.ac

@@ -1905,7 +1905,7 @@ if test x$need_bundled_univalue = xyes; then
   AC_CONFIG_SUBDIRS([src/univalue])
 fi
 
-ac_configure_args="${ac_configure_args} --disable-shared --with-pic --enable-benchmark=no --with-bignum=no --enable-module-recovery --enable-module-schnorrsig --enable-experimental"
+ac_configure_args="${ac_configure_args} --disable-shared --with-pic --enable-benchmark=no --enable-module-recovery --enable-module-schnorrsig --enable-experimental"
 AC_CONFIG_SUBDIRS([src/secp256k1])
 
 AC_OUTPUT