build: Drop dead non-pkg-config code for UNIVALUE check

configure.ac

@@ -1371,24 +1371,7 @@ if test x$build_bitcoin_wallet$build_bitcoin_cli$build_bitcoin_tx$build_bitcoind
 else
 
 if test x$system_univalue != xno ; then
-  found_univalue=no
-  if test x$use_pkgconfig = xyes; then
-    : #NOP
-    m4_ifdef(
-      [PKG_CHECK_MODULES],
-      [
-        PKG_CHECK_MODULES([UNIVALUE],[libunivalue >= 1.0.4],[found_univalue=yes],[true])
-      ]
-    )
-  else
-    AC_CHECK_HEADER([univalue.h],[
-      AC_CHECK_LIB([univalue],  [main],[
-        UNIVALUE_LIBS=-lunivalue
-        found_univalue=yes
-      ],[true])
-    ],[true])
-  fi
-
+  PKG_CHECK_MODULES([UNIVALUE], [libunivalue >= 1.0.4], [found_univalue=yes], [found_univalue=no])
   if test x$found_univalue = xyes ; then
     system_univalue=yes
     need_bundled_univalue=no