refactor(core): finally remove Core::getInstance

This makes Core completly independent of Nexus

src/core/core.cpp

@@ -29,7 +29,6 @@
 #include "src/model/groupinvite.h"
 #include "src/model/status.h"
 #include "src/model/ibootstraplistgenerator.h"
-#include "src/nexus.h"
 #include "src/persistence/profile.h"
 #include "util/strongtype.h"
 
@@ -705,15 +704,6 @@ void Core::start()
     coreThread->start();
 }
 
-
-/**
- * @brief Returns the global widget's Core instance
- */
-Core* Core::getInstance()
-{
-    return Nexus::getCore();
-}
-
 const CoreAV* Core::getAv() const
 {
     return av.get();

src/core/core.h

@@ -71,7 +71,6 @@ public:
 
     static ToxCorePtr makeToxCore(const QByteArray& savedata, const ICoreSettings* const settings,
                                   IBootstrapListGenerator& bootstrapNodes, ToxCoreErrors* err = nullptr);
-    static Core* getInstance();
     const CoreAV* getAv() const;
     CoreAV* getAv();
     CoreFile* getCoreFile() const;