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

configure.ac

@@ -1302,9 +1302,6 @@ if test x$use_pkgconfig = xyes; then
   m4_ifdef(
     [PKG_CHECK_MODULES],
     [
-      if test x$use_qr != xno; then
-        BITCOIN_QT_CHECK([PKG_CHECK_MODULES([QR], [libqrencode], [have_qrencode=yes], [have_qrencode=no])])
-      fi
       if test x$build_bitcoin_cli$build_bitcoind$bitcoin_enable_qt$use_tests$use_bench != xnonononono; then
         PKG_CHECK_MODULES([EVENT], [libevent >= 2.0.21], [use_libevent=yes], [AC_MSG_ERROR(libevent version 2.0.21 or greater not found.)])
         if test x$TARGET_OS != xwindows; then
@@ -1322,11 +1319,12 @@ else
       AC_CHECK_LIB([event_pthreads],[main],EVENT_PTHREADS_LIBS=-levent_pthreads,AC_MSG_ERROR(libevent_pthreads missing))
     fi
   fi
+fi
 
-  if test x$use_qr != xno; then
-    BITCOIN_QT_CHECK([AC_CHECK_LIB([qrencode], [main],[QR_LIBS=-lqrencode], [have_qrencode=no])])
-    BITCOIN_QT_CHECK([AC_CHECK_HEADER([qrencode.h],, have_qrencode=no)])
-  fi
+dnl QR Code encoding library check
+
+if test "x$use_qr" != xno; then
+  BITCOIN_QT_CHECK([PKG_CHECK_MODULES([QR], [libqrencode], [have_qrencode=yes], [have_qrencode=no])])
 fi
 
 dnl ZMQ check