Use anonymous namespace for constants

src/collection/collectionfilterwidget.cpp

@@ -61,6 +61,10 @@
 #include "settings/collectionsettingspage.h"
 #include "settings/appearancesettingspage.h"
 
+namespace {
+constexpr int kFilterDelay = 500;  // msec
+}
+
 CollectionFilterWidget::CollectionFilterWidget(QWidget *parent)
     : QWidget(parent),
       ui_(new Ui_CollectionFilterWidget),

src/collection/collectionfilterwidget.h

@@ -51,8 +51,6 @@ class CollectionFilterWidget : public QWidget {
   explicit CollectionFilterWidget(QWidget *parent = nullptr);
   ~CollectionFilterWidget() override;
 
-  static const int kFilterDelay = 500;  // msec
-
   enum class DelayBehaviour {
     AlwaysInstant,
     DelayedOnLargeLibraries,