core/loader: Remove dependencies on the global system instance

Now all that remains is:

18 instances in file_sys code
14 instances in GDB stub code (this can be tossed wholesale)
4 instances in HLE code
2 instances in settings code.

src/core/loader/nro.h

@@ -10,6 +10,10 @@
 #include "common/common_types.h"
 #include "core/loader/loader.h"
 
+namespace Core {
+class System;
+}
+
 namespace FileSys {
 class NACP;
 }
@@ -37,7 +41,7 @@ public:
         return IdentifyType(file);
     }
 
-    LoadResult Load(Kernel::Process& process) override;
+    LoadResult Load(Kernel::Process& process, Core::System& system) override;
 
     ResultStatus ReadIcon(std::vector<u8>& buffer) override;
     ResultStatus ReadProgramId(u64& out_program_id) override;