yuzu: Remove usage of the global telemetry accessor

In these cases the system object is nearby, and in the other, the
long-form of accessing the telemetry instance is already used, so we can
get rid of the use of the global accessor.

src/yuzu/main.cpp

@@ -846,7 +846,7 @@ bool GMainWindow::LoadROM(const QString& filename) {
     }
     game_path = filename;
 
-    Core::Telemetry().AddField(Telemetry::FieldType::App, "Frontend", "Qt");
+    system.TelemetrySession().AddField(Telemetry::FieldType::App, "Frontend", "Qt");
     return true;
 }