service: Eliminate usages of the global system instance

Completely removes all usages of the global system instance within the
services code by passing in the using system instance to the services.

src/core/hle/service/glue/bgtc.h

@@ -6,17 +6,21 @@
 
 #include "core/hle/service/service.h"
 
+namespace Core {
+class System;
+}
+
 namespace Service::Glue {
 
 class BGTC_T final : public ServiceFramework<BGTC_T> {
 public:
-    BGTC_T();
+    explicit BGTC_T(Core::System& system_);
     ~BGTC_T() override;
 };
 
 class BGTC_SC final : public ServiceFramework<BGTC_SC> {
 public:
-    BGTC_SC();
+    explicit BGTC_SC(Core::System& system_);
     ~BGTC_SC() override;
 };