[libcontacts] Avoid fallback to non-name details when grouping

Including this fallback option leads to the following undesirable
scenario:
  1. contact details yield a group which is not in the allGroups set
  2. the contact is originally grouped in the '#' group
  3. when the contact's addresses are later retrieved, the fallback
     code re-classifies the contact under a group derived from a
     non-name property of the contact
  4. the contact is no longer visible under the original group; the
     new group has no connection to the contact's displayed name,
     and cannot be reliably predicted by the user

src/seasidecache.cpp

@@ -718,15 +718,10 @@ QString SeasideCache::determineNameGroup(const CacheItem *cacheItem)
     QString group;
     if (!nameProperty.isEmpty()) {
         group = mLocale.indexBucket(nameProperty);
-    } else  if (!cacheItem->displayLabel.isEmpty()) {
+    } else if (!cacheItem->displayLabel.isEmpty()) {
         group = mLocale.indexBucket(cacheItem->displayLabel);
     }
 
-    if (group.isNull() || !allContactNameGroups.contains(group)) {
-        QString displayLabel = generateDisplayLabelFromNonNameDetails(cacheItem->contact);
-        if (!displayLabel.isEmpty())
-            group = mLocale.indexBucket(displayLabel);
-    }
     if (group.isNull() || !allContactNameGroups.contains(group)) {
         group = QString::fromLatin1("#");   // 'other' group
     }