mem: Remove the unused nvm private member from NVMInterface::Rank.

This unused (and otherwise unusable) member caused a compiler warning
and broke the build for me. It can be reintroduced if used in the
future.

Change-Id: I48181f6bca60c059e74727290950adfb9a194680
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/34217
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/mem/mem_interface.cc

@@ -2043,8 +2043,7 @@ NVMInterfaceParams::create()
 
 NVMInterface::Rank::Rank(const NVMInterfaceParams* _p,
                          int _rank, NVMInterface& _nvm)
-    : EventManager(&_nvm), nvm(_nvm), rank(_rank),
-      banks(_p->banks_per_rank)
+    : EventManager(&_nvm), rank(_rank), banks(_p->banks_per_rank)
 {
     for (int b = 0; b < _p->banks_per_rank; b++) {
         banks[b].bank = b;

src/mem/mem_interface.hh

@@ -1026,13 +1026,6 @@ class NVMInterface : public MemInterface
      */
     class Rank : public EventManager
     {
-      private:
-
-        /**
-         * A reference to the parent NVMInterface instance
-         */
-        NVMInterface& nvm;
-
       public:
 
         /**