[qofbook.cpp] backport qof_book_unset_feature from master

libgnucash/engine/qofbook.cpp

@@ -1285,6 +1285,22 @@ qof_book_test_feature (QofBook *book, const char *feature)
     return (frame->get_slot({GNC_FEATURES, feature}) != nullptr);
 }
 
+void
+qof_book_unset_feature (QofBook *book, const gchar *key)
+{
+    KvpFrame *frame = qof_instance_get_slots (QOF_INSTANCE (book));
+    auto feature_slot = frame->get_slot({GNC_FEATURES, key});
+    if (!feature_slot)
+    {
+        PWARN ("no feature %s. bail out.", key);
+        return;
+    }
+    qof_book_begin_edit (book);
+    delete frame->set_path({GNC_FEATURES, key}, nullptr);
+    qof_instance_set_dirty (QOF_INSTANCE (book));
+    qof_book_commit_edit (book);
+}
+
 void
 qof_book_load_options (QofBook *book, GNCOptionLoad load_cb, GNCOptionDB *odb)
 {

libgnucash/engine/qofbook.h

@@ -382,6 +382,7 @@ void qof_book_option_frame_delete (QofBook *book, const char* opt_name);
 /** Access functions for reading and setting the used-features on this book.
  */
 GHashTable *qof_book_get_features (QofBook *book);
+void qof_book_unset_feature (QofBook *book, const gchar *key);
 void qof_book_set_feature (QofBook *book, const gchar *key, const gchar *descr);
 
 void qof_book_begin_edit(QofBook *book);