[lld] [lld][WebAssembly] Match the ELF linker in transitioning away from archive indexes. (PR #78658)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> The ELF linker transitioned away from archive indexes in [reviews.llvm.org/D117284](https://reviews.llvm.org/D117284).

This patch also removes `ArchiveFile`. The ELF reference probably should be https://reviews.llvm.org/D119074 (`[ELF] Parse archives as --start-lib object files`).

https://github.com/llvm/llvm-project/pull/78658