[lld] [ELF] Rename LazyObject to LazySymbol. NFC (PR #78809)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> (Should the title prefix be `[lld][ELF]`?)

I follow George Rimar and some others' convention by using just `[ELF]`. It's like for many llvm and clang changes, many people don't use `[llvm]` or `[clang]`. This makes sense, because you need `git log -- llvm` to figure out llvm/ changes to not bother with other changes, and the `[llvm]` tag is not very helpful when I run git log this way. I think the `XXX` in `llvm/lib/XXX` `clang/lib/XXX` part is more useful. However, I see that many people add the XXX in `llvm-project/XXX` as a tag. I think it's different preference.

https://github.com/llvm/llvm-project/pull/78809