Remove History::optimizeHistory() function

It is no longer needed, this function was little confusing
as it actually only executed VACUUM.
Instead, execute VACUUM after clearing all history in
History::clearHistory()

src/lib/history/history.cpp

@@ -241,15 +241,13 @@ bool History::optimizeHistory()
     return query.exec("VACUUM");
 }
 
-bool History::clearHistory()
+void History::clearHistory()
 {
     QSqlQuery query;
-    if (query.exec("DELETE FROM history")) {
-        emit resetHistory();
-        return true;
-    }
+    query.exec(QSL("DELETE FROM history"));
+    query.exec(QSL("VACUUM"));
 
-    return false;
+    emit resetHistory();
 }
 
 void History::setSaving(bool state)

src/lib/history/history.h

@@ -62,7 +62,7 @@ public:
 
     QVector<HistoryEntry> mostVisited(int count);
 
-    bool clearHistory();
+    void clearHistory();
     bool optimizeHistory();
     bool isSaving();
     void setSaving(bool state);

src/lib/history/historymanager.cpp

@@ -81,7 +81,6 @@ void HistoryManager::clearHistory()
     }
 
     mApp->history()->clearHistory();
-    mApp->history()->optimizeHistory();
 }
 
 void HistoryManager::search(const QString &searchText)