[llvm] [lit] Add type hints to builtin_commands (PR #201497)

[via llvm-commits]

prasoon054 wrote:

Removed the redundant annotations. Also dropped the unused `filelines` in `diff.main()`. It was only created by `([] for i in range(3))` unpack and never read.

https://github.com/llvm/llvm-project/pull/201497