made appbase compile standalone

src/util/FunctionEventFilter.cpp

@@ -1,17 +0,0 @@
-#include "FunctionEventFilter.hpp"
-
-namespace chatterino {
-
-FunctionEventFilter::FunctionEventFilter(
-    QObject *parent, std::function<bool(QObject *, QEvent *)> function)
-    : QObject(parent)
-    , function_(std::move(function))
-{
-}
-
-bool FunctionEventFilter::eventFilter(QObject *watched, QEvent *event)
-{
-    return this->function_(watched, event);
-}
-
-}  // namespace chatterino