[libc++] NFCI: Remove dead code in the Lit configuration

I was trying to fix something else and I stumbled upon several methods
that are not used anymore in target_info.py.

Differential Revision: https://reviews.llvm.org/D98896

GitOrigin-RevId: 976eba51d0dea36b9e0e4f6edb09883490f79684
1 file changed