cpu,fastmodel: Get rid of unused (read|set)FuncExeInst.

These zombie methods were plumbed around and looked like they might do
something, but nothing actually uses them.

Change-Id: I1e85669202e2ecb10370e6c6eb8364eb47085cf3
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/45919
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabe.black@gmail.com>

src/cpu/simple_thread.cc

@@ -95,7 +95,6 @@ SimpleThread::takeOverFrom(ThreadContext *oldContext)
 
     isa->takeOverFrom(this, oldContext);
 
-    funcExeInst = oldContext->readFuncExeInst();
     storeCondFailures = 0;
 }
 
@@ -105,8 +104,6 @@ SimpleThread::copyState(ThreadContext *oldContext)
     // copy over functional state
     _status = oldContext->status();
     copyArchRegs(oldContext);
-    if (FullSystem)
-        funcExeInst = oldContext->readFuncExeInst();
 
     _threadId = oldContext->threadId();
     _contextId = oldContext->contextId();