Disable building libzcashconsensus by default

The library is not currently a supported build artifact; it needs work in
order to build on certain platforms (e.g. MacOS), and its dependencies need to
be narrowed down (Equihash is not a requirement for validating scripts).

configure.ac

@@ -224,9 +224,9 @@ AC_ARG_WITH([utils],
 
 AC_ARG_WITH([libs],
   [AS_HELP_STRING([--with-libs],
-  [build libraries (default=yes)])],
+  [build libraries (default=no)])],
   [build_bitcoin_libs=$withval],
-  [build_bitcoin_libs=yes])
+  [build_bitcoin_libs=no])
 
 AC_ARG_WITH([daemon],
   [AS_HELP_STRING([--with-daemon],