[llvm] [MC] Remove a redundant declaration of createNullStreamer (NFC) (PR #166025)

[Kazu Hirata via llvm-commits]

kazutakahirata wrote:

> Well, I think this is just a forward declaration such that the header doesn't need to be included. Not sure how this will help.

To be honest, I was a little bit on the fence.  We do have a policy for forward declarations of classes and structs, but I wasn't sure about forward declarations of functions.  I'm closing this PR.  Thanks for the review anyway!


https://github.com/llvm/llvm-project/pull/166025