[llvm] Removed expansive copy (PR #93658)

[Malay Sanghi via llvm-commits]

MalaySanghi wrote:

Looking at 
https://en.cppreference.com/w/cpp/language/structured_binding
section: binding a tuple-like type

and then at the definition of enumerate
```
auto enumerate(FirstRange &&First, RestRanges &&...Rest)
```

I think M and I are already references. I don't think we need this change. 

https://github.com/llvm/llvm-project/pull/93658