[llvm] RISCV: Remove shouldForceRelocation and unneeded relocations (PR #140692)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Ready for review:) This cleans up tech debt in our relocation generation, which I hope we get in before introducing more stuff to `addReloc`.

I will do a rebase soon to re-trigger CI.

https://github.com/llvm/llvm-project/pull/140692