chore: remove Singleton & replace getIApp with getApp (#5514)

src/singletons/CrashHandler.hpp

@@ -1,7 +1,5 @@
 #pragma once
 
-#include "common/Singleton.hpp"
-
 #include <QtGlobal>
 
 #ifdef CHATTERINO_WITH_CRASHPAD
@@ -15,7 +13,7 @@ namespace chatterino {
 class Args;
 class Paths;
 
-class CrashHandler : public Singleton
+class CrashHandler
 {
     const Paths &paths;
 
@@ -30,8 +28,6 @@ public:
     /// Sets and saves whether Chatterino should restart on a crash
     void saveShouldRecover(bool value);
 
-    void initialize(Settings &settings, const Paths &paths) override;
-
 private:
     bool shouldRecover_ = false;
 };