[libcxx] [llvm] [LIT] remove `to_unicode`, `to_string`, and `to_bytes` helpers (PR #165950)

[Alexander Richardson via llvm-commits]

arichardson wrote:

Does that mean we don't run lldb tests as part of pre-submit? At least the fix looks trivial so hopefully not too much breakage. 

https://github.com/llvm/llvm-project/pull/165950