[llvm] Revert "[FileCheck] Add a diff output option for FileCheck (#187120)" (PR #192803)

[Fangrui Song via llvm-commits]

MaskRay wrote:

FTR, I’m very much in favor of this feature, but we should ensure the initial version is stable and free of major issues before merging.

https://github.com/llvm/llvm-project/pull/192803