Remove explicit copy assignment operator in favor of the implicit/default to avoid disabling/deprecating the implicit copy ctor.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231109 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/AliasSetTracker.h

@@ -192,11 +192,6 @@ public:
     }
     bool operator!=(const iterator& x) const { return !operator==(x); }
 
-    const iterator &operator=(const iterator &I) {
-      CurNode = I.CurNode;
-      return *this;
-    }
-
     value_type &operator*() const {
       assert(CurNode && "Dereferencing AliasSet.end()!");
       return *CurNode;