FEXCore/Context: Removes InitialRIP/RSP from CreateThread

We actually never use this anymore, we instead always pass zero for
both, and then rely on the thread inheritance model or setting the
values manually. Now that we expose visibility of the
InternalThreadState to the frontend they just access it directly.

Just a smidge of cleanup, NFC.

Source/Windows/ARM64EC/Module.cpp

@@ -922,7 +922,7 @@ NTSTATUS ThreadInit() {
   CPUArea.EmulatorStackLimit() = EmulatorStack;
   CPUArea.EmulatorStackBase() = EmulatorStack + EmulatorStackSize;
 
-  auto* Thread = CTX->CreateThread(0, 0);
+  auto* Thread = CTX->CreateThread();
 
   // Default segment setup.
   auto Frame = Thread->CurrentFrame;