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/thread_context.hh

@@ -268,9 +268,6 @@ class ThreadContext : public PCEventScope
 
     virtual void setStCondFailures(unsigned sc_failures) = 0;
 
-    // Same with st cond failures.
-    virtual Counter readFuncExeInst() const = 0;
-
     // This function exits the thread context in the CPU and returns
     // 1 if the CPU has no more active threads (meaning it's OK to exit);
     // Used in syscall-emulation mode when a  thread calls the exit syscall.