chore: unsingletonize UserDataController (#5459)

The `user-data.json` file will save immediately on change, and on exit
(on dtor) if necessary. So we don't need to manually call save

src/controllers/userdata/UserDataController.hpp

@@ -1,6 +1,5 @@
 #pragma once
 
-#include "common/Singleton.hpp"
 #include "controllers/userdata/UserData.hpp"
 #include "util/QStringHash.hpp"
 #include "util/RapidjsonHelpers.hpp"
@@ -30,7 +29,7 @@ public:
                               const QString &colorString) = 0;
 };
 
-class UserDataController : public IUserDataController, public Singleton
+class UserDataController : public IUserDataController
 {
 public:
     explicit UserDataController(const Paths &paths);
@@ -43,9 +42,6 @@ public:
     void setUserColor(const QString &userID,
                       const QString &colorString) override;
 
-protected:
-    void save() override;
-
 private:
     void update(std::unordered_map<QString, UserData> &&newUsers);