[lld] [lld][COFF] Remove duplicate strtab entries (PR #141197)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Test needed. In ELF we can use `llvm-readelf -p .strtab` to dump the section table. I don't know what the COFF counterpart is.

https://github.com/llvm/llvm-project/pull/141197