[llvm-exegesis] Remove unnecessary deletion of an assignment operator of WrappingIterator that angers some versions of MSVC

The deletion of the const WrappingIterator & should already cover this.

llvm/tools/llvm-exegesis/lib/SnippetGenerator.h

@@ -150,7 +150,6 @@ class CombinationGenerator {
     WrappingIterator() = delete;
     WrappingIterator(const WrappingIterator &) = delete;
     WrappingIterator(WrappingIterator &&) = delete;
-    WrappingIterator &operator=(WrappingIterator) = delete;
     WrappingIterator &operator=(const WrappingIterator &) = delete;
     WrappingIterator &operator=(WrappingIterator &&) = delete;
   };