hle/service: Resolve unused variable warnings

In several places, we have request parsers where there's nothing to
really parse, simply because the HLE function in question operates on
buffers. In these cases we can just remove these instances altogether.

In the other cases, we can retrieve the relevant members from the parser
and at least log them out, giving them some use.

src/core/hle/service/spl/module.cpp

@@ -26,9 +26,7 @@ Module::Interface::~Interface() = default;
 void Module::Interface::GetRandomBytes(Kernel::HLERequestContext& ctx) {
     LOG_DEBUG(Service_SPL, "called");
 
-    IPC::RequestParser rp{ctx};
-
-    std::size_t size = ctx.GetWriteBufferSize();
+    const std::size_t size = ctx.GetWriteBufferSize();
 
     std::uniform_int_distribution<u16> distribution(0, std::numeric_limits<u8>::max());
     std::vector<u8> data(size);