[llvm] [unused-includes][ADT] Don't include DJB.h as it's not used. NFC. (PR #88211)

[David Blaikie via llvm-commits]

https://github.com/dwblaikie approved this pull request.

Thanks for the catch! Must've been a holdover from the original version of the patch.

https://github.com/llvm/llvm-project/pull/88211