CPU: Get rid of the now unnecessary getInst/setInst family of functions.

This code is no longer needed because of the preceeding change which adds a
StaticInstPtr parameter to the fault's invoke method, obviating the only use
for this pair of functions.

src/cpu/simple_thread.cc

@@ -181,7 +181,6 @@ SimpleThread::copyState(ThreadContext *oldContext)
 #if !FULL_SYSTEM
     funcExeInst = oldContext->readFuncExeInst();
 #endif
-    inst = oldContext->getInst();
 
     _threadId = oldContext->threadId();
     _contextId = oldContext->contextId();